A gantry crane travels further than any machine in the plant, and the power has to follow it. Transformer, cable, reel and earth, measured on the runway rather than on the nameplate.
Most crane electrical questions have one answer. On a special crane the same question has four, and they contradict each other. A conductor bar that is the cheapest and most reliable way to power a 20 tonne grab crane is not permitted at all in the shed next door if that shed is classified. A drive that improves control on a pickling line can void the certification of the motor two metres away. A hoist that is perfectly safe in a coal shed will fail a particle count in a cleanroom.
So the supply decision on a special crane is not a load calculation. It is a room calculation. Get the room wrong and the electrical package is wrong no matter how well it is sized.
This article walks the four rooms we build for: bulk handling in combustible dust, pickling and acid lines, cleanrooms, and gas-rated plant. Same crane family, same controller, four different answers. Installed capacity across those rooms runs from about 0.5 tonne in a semiconductor bay to 50 tonne on a grab.
Because the failure mode changes. On an ordinary crane the enemy is voltage drop and duty class. In a hazardous area the enemy is a spark you cannot see, or a surface at 140 degrees when the gas ignites at 135. In a pickling hall the enemy is a film of hydrochloric acid that turns a clean insulator into a conductor over eighteen months. In a cleanroom the enemy is the carbon dust coming off your own collector shoes.
Each of those is an electrical problem with a mechanical answer, or the other way round. That is why the electrical package on a special crane is usually the second largest line on the quote after the structure.
| Room | What the atmosphere does | What fails first | What the supply has to be |
|---|---|---|---|
| Grab, bulk terminal | Combustible dust cloud, 5 mm layer on every horizontal surface | Surface temperature under the dust layer, not the arc | Dust-rated enclosure, IP6X, declared T-class with the layer |
| Pickling line | Acid mist, condensation twice a day, chloride film | Insulation resistance, then creepage tracking | IP65 or better, pollution degree 3 or 4 assumed, sheath that resists the acid |
| Cleanroom | Nothing corrosive. Everything counts particles instead | The crane as a particle and ESD source | Sealed drive, filtered motor air, no exposed sliding contact |
| Gas-rated plant | Flammable gas or vapour, Zone 1 or 2 | Any sparking contact, any hot surface | Ex-rated motor and collector, no open conductor bar at all |
Notice that only one of those four columns mentions electricity in the normal sense. Three of them are about what the environment does to the equipment, not what the equipment does to the supply.
The rooms get names from the zone system, not from the process. Gas zones are 0, 1 and 2. Dust zones are 20, 21 and 22. The number tracks how often the atmosphere is actually present, and the figures below are the ones the crane makers publish on their Ex marking sheets.
| Zone | Presence per year | ATEX category | Enclosure for dust |
|---|---|---|---|
| 0 / 20 | Over 1,000 hours | Category 1 | IP6X, and most crane builders will not quote it |
| 1 / 21 | 10 to 1,000 hours | Category 2 | IP6X, conductive or not |
| 2 / 22 | Under 10 hours | Category 3 | IP6X if the dust conducts, IP5X if it does not |
Two things trip people up here. The first is that the IP requirement is not a blanket number. In Zone 22 you may use IP5X when the dust is non-conductive and IP6X when it is conductive, so a grain terminal and a metal powder plant in the same Zone 22 category do not get the same enclosure. The second is that a Category 3 crane is not a Category 2 crane with fewer certificates. The tested faults are different, and the paperwork is different.
Surface temperature comes on top of the zone. Gas classes run T1 at 450 degrees down to T6 at 85, and most industrial buyers ask for T3 or T4. T4 is 135 degrees. That single number decides more of the electrical package than the zone does, because it applies to the outside of the motor, the inside of the terminal box, and the brake.
| Class | Max surface | Typical gas | What it costs you |
|---|---|---|---|
| T1 | 450 C | Ammonia, methane in some grades | Almost nothing. Standard motors pass |
| T3 | 200 C | Petrol vapour, most solvents | Real. Motor class, brake type, terminal box |
| T4 | 135 C | Acetaldehyde, diethyl ether, most refinery streams | Drives the whole motor selection, and rules out most standard brakes |
| T6 | 85 C | Carbon disulphide | Special machines only. We decline more of these than we take |
A 30 kW motor at 85 degrees surface is not a 30 kW motor with a bigger fan. It is a different frame, a different winding, often a different cooling method. If the buyer writes T6 in the specification without checking what is in the room, the project stalls at the motor quotation stage and everybody loses six weeks.
This one is not a matter of opinion. Mazzella, who have been electrifying cranes for decades, put it in a single sentence in their comparison of conductor bars, festoon and cable reels: a conductor bar system can never be used in an environment that requires an explosion proof crane.
The reason is the collector shoe. It is a sliding contact. It sparks a little at every joint, every time the crane passes, and under load it sparks more. In an ordinary shed that spark is a maintenance nuisance. In a Zone 1 atmosphere it is an ignition source with a lifetime measured in milliseconds.
You cannot seal your way out of it either. An enclosed conductor bar with an IP6X cover still has a sliding shoe running on a bare conductor inside the cover, and the standard does not accept an enclosure as protection for a sparking contact in a classified atmosphere. That is why the answer is not a better conductor bar. The answer is a different technology.
The same logic runs through the accessories. Conductix-Wampfler's own ATEX festoon catalogue sets a maximum running speed of 1 m/s and states plainly that explosion protection is void above that speed. It also bans PVC cables and hoses in the system and requires heavy polychloroprene or an equivalent synthetic elastomer sheath. Both of those requirements are there for the same reason: static build-up and sheath breakdown produce sparks that no enclosure will contain.
Three options, and they are not interchangeable. Festoon, cable reel, and an Ex-rated slip ring if the machine rotates.
| Method | Speed limit | Sheath and materials | Where it wins |
|---|---|---|---|
| ATEX festoon | 1 m/s, hard limit | Heavy polychloroprene. No PVC anywhere | Short to medium runways, trolley and bridge, control included |
| Cable reel | Set by reel and cable, 60 to 100 m/min typical | Stainless or galvanised steel body, powder coated | Long travel, corrosive and acidic rooms, high cycle counts |
| Ex slip ring | Rotation, typically 40 rpm and up on request | Flameproof or increased safety housing, IP65 or IP66 | Slewing machines, stackers, any continuous rotation |
Festoon carries the most cable for the least money and it is the default for a Zone 1 bridge. The 1 m/s limit sounds restrictive until you check the actual long travel speed, which on a 20 tonne process crane is often 20 to 40 m/min, or 0.33 to 0.67 m/s. The limit bites on high-speed grabbing cranes and on long runways where you would rather not drag 40 m of cable.
The cable reel is the answer in the pickling hall, and not only for the explosion side. Stainless or galvanised construction with a coated body is the only thing that survives an acid atmosphere for a decade. Mazzella specifically names corrosive and acidic environments as a reel application, which is the opposite of what most people assume. We have replaced more festoons than reels on acid lines.
The slip ring is the fourth option and the one buyers forget. If the machine rotates, the power has to cross a rotating joint, and on an Ex machine that joint is a certified component, not a standard one. The Italian maker TER publishes an Ex slip ring rated IP65 or IP66 over minus 40 to plus 60 degrees, up to 150 A on the small frame and 638 A on the large one, at up to 1,000 V and 6,000 V respectively, certified to the ATEX directive and to EN 60079-0, EN 60079-1 and EN 60079-14 with IECEx as well. Trolex builds the same idea for Zone 1 as a flameproof Group IIB unit, IP66, 400 A throughput at 1,000 V AC, 40 rpm, with a self-regulating anti-condensation heater built in and a minimum of two brushes per ring. Note the brush split: copper-graphite for power, silver-graphite for signals.
This is the single most expensive misunderstanding in the whole package, and it is not the buyer's fault. Most drives are sold as general purpose products, most Ex motors are sold as motors, and the combination is treated as a wiring detail. It is not.
ABB's own guidance on motors and drives in explosive atmospheres sets out what each protection type needs before a drive can be connected. It is worth reading in their words rather than mine, but the shape is this:
| Protection type | What has to be true before a drive is allowed | Practical effect on the order |
|---|---|---|
| Ex d, flameproof | Motor tested with the drive for the duty and with the protective device, or direct temperature protection with embedded sensors and margin | The drive model becomes part of the certificate. Swap it and the file is dead |
| Ex ec, increased safety | Tested with the drive or a comparable drive, or temperature class by calculation, or direct control from embedded sensors | Workable. The calculation or the sensor route is normally the cheaper path |
| Ex eb | Tested together with the specific drive and protective device. A combined heat run test is mandatory | No shortcuts. This is a factory test, not a calculation |
The protective device route is the one most projects end up using, and it has a detail that gets missed. Drives can carry an integrated safe motor temperature function, defined in EN and IEC 61800-5-2, and that function is certified as a protective device under ATEX. But the marking on that drive refers only to the safety function inside it, not to the drive being tested with your motor. And because those drives do not normally have an Ex enclosure, they can only be installed outside the hazardous area. On the certificate this shows up as a bracketed category, for example (2), which reads as a device intended to be mounted outside the zone.
So the question to ask is not "is this drive ATEX certified". The question is "what is the certificate for, and where does the box physically sit". Those have different answers and they change the panel layout.
The T-class is not a property of the motor. It is a property of the motor at a particular operating point, and the operating point that matters is rarely the nameplate one.
A standard totally enclosed fan cooled motor carries a shaft-mounted fan. At rated speed the fan moves enough air to hold the winding temperature down. At 10 percent of rated speed it moves almost nothing, because fan flow falls roughly with speed while the losses inside the motor stay close to full value under load. The winding gets hotter at 5 Hz than it ever gets at 50 Hz, at the same torque.
That is the whole reason the standards make such a fuss about the drive-motor combination. A motor that holds T4 at 1,500 rpm will not necessarily hold T4 at 75 rpm with the same load, and no amount of drive configuration changes the airflow. What the drive can do is measure and act: read the PTC or PT100 in the winding, model the thermal state, and disconnect before the surface goes over the limit. ABB's guidance lists exactly that as the alternative to a tested combination, and notes that limiting the switching frequency through the Ex parameters derates available current, which has to be in the calculation.
Three practical routes, in order of cost:
The first is a separate forced-ventilation blower on the motor, interlocked with the drive. Cheap, ugly, effective, and the standard answer on machine tools. It removes the variable entirely.
The second is a drive with a certified thermal function and a PT100 in the winding, with the trip set to the class limit rather than to the insulation class. This is cheaper than a blower on a small machine and needs commissioning discipline, because the default parameters are set for a standard motor.
The third is to accept a larger frame size so that the derated continuous torque still covers the duty. On a grabbing crane with a 40 percent duty cycle this is often the cleanest answer, and it is the one that survives an audit five years later.
Whichever route you take, the acceptance document is a heat run at the lowest speed the crane will actually run, at the highest load it will actually carry, with the surface temperature measured rather than assumed. We have seen a T4 grab crane pass that test at 50 Hz and fail it at 6 Hz, in the same afternoon, with nothing changed but the speed reference.
Slowly, and then you measure it. The rails look like the most obvious earth path in the building and they are the one you cannot rely on. Wheels are not a bonding conductor. Wheel-to-rail contact depends on load, on rust, on grease, and on whether the crane happens to be sitting over a joint. At the moment you need the bond most, the crane may be unloaded and the contact resistance may be tens of ohms.
So the bonding is a copper conductor, not a bearing surface. IEC TS 60079-32-1 puts a number on it in section 13.2.2: metallic items in good contact with earth should have a resistance to it of less than 10 ohms, and while up to 1 megohm is acceptable for dissipating static, values above 10 ohms are an early indicator of corrosion or a loose connection and should be investigated. NFPA 77 is consistent, quoting about 10 ohms for copper and 25 ohms for stainless steel in practice.
| Bonding point | Target | What we actually see on site |
|---|---|---|
| Festoon rail to building earth | Under 10 ohms | Usually fine. Painted brackets are the exception |
| Bridge to runway rail | Continuous copper bond | Missing on about one crane in five. Wheels were assumed to be enough |
| Trolley to bridge | Continuous copper bond | Frequently routed through the festoon trolley instead of a dedicated strap |
| Hoist frame to trolley | Continuous copper bond | Missed when the hoist is supplied separately and bolted on at site |
| Grab or lifting attachment | Bonded, not hung on the rope | The most commonly forgotten bond on a grab crane |
Test it with a proper low-resistance instrument, not a multimeter on the ohms range. Record the values, because the second reading a year later is the one that tells you whether a joint is corroding. And test at the joints, not only end to end: a good end-to-end reading can hide a strap that is carrying current through a bearing.
Dust settles, insulates, and burns. Gas disperses and ignites. That difference changes the calculation in two ways.
The first is the enclosure. Dust has to be kept out of the box, which is an IP problem, and the requirement is not uniform. In Zone 21 both conductive and non-conductive dust require IP6X. In Zone 22 you may use IP5X for non-conductive dust but IP6X for conductive dust. A metal powder plant and a flour mill can both be Zone 22 and they cannot both use the same enclosure.
The second is the surface temperature, and this is where dust is subtler than gas. For gas you compare the surface against the ignition temperature of the gas. For dust you have to consider the cloud and the layer separately, because a 5 mm layer of dust insulates the surface and lets it run hotter than the same equipment would run clean.
| Step | Formula | Worked example |
|---|---|---|
| Cloud limit | Two thirds of the cloud ignition temperature | Cloud ignites at 450 C, limit becomes 300 C |
| Layer limit | Layer ignition temperature minus 75 K | Layer ignites at 300 C, limit becomes 225 C |
| Governing value | The lower of the two | 225 C, so the equipment is marked T3 or better |
| Ambient correction | Declared at 40 C unless the nameplate says otherwise | A 55 C shed needs a re-rated machine, not a note on the drawing |
Note what that table means for a crane. The motor is not the only hot surface. The brake is hot every time it stops. So is the resistor, if there is one, and the contactor arc chutes. On a dust-rated grab crane we mark the brake and the resistor separately, because the motor certificate does not cover them.
And a dust layer on top of a panel is a thermal problem even when it is not an ignition problem. A 5 mm layer roughly doubles the thermal resistance of the panel wall. That is why the derating on a dusty site is bigger than the dust specification alone suggests.
Because acid does not attack the metal first. It attacks the surface of the insulation, and it does it slowly enough that nobody notices until the earth leakage relay trips on a machine that has run for three years.
The mechanism is creepage tracking. A film of chloride on an insulator is mildly conductive, and in a humid hall with condensation twice a day, that film becomes a leakage path across the surface. Once a carbon track forms it does not heal. The IEC 60664-1 framework puts a name on this with the pollution degree, and a pickling hall is pollution degree 3 at best and 4 in the splash zone. For reference, the standard imposes minimum creepage floors of 0.2 mm at degree 2, 0.8 mm at degree 3 and 1.6 mm at degree 4, independent of voltage, because a small gap can be bridged by a droplet or a particle whatever the voltage is.
| Item | Standard build | What an acid line needs |
|---|---|---|
| Panel | IP54, painted steel | IP65 or IP66, 304 or 316 stainless, sloped top, no horizontal ledge |
| Condensation | Not addressed | Anti-condensation heater with its own thermostat, plus breather drain |
| Cable sheath | PVC | Polychloroprene or equivalent. PVC embrittles and cracks at glands |
| Glands and fixings | Nickel plated brass | 316 stainless, or the gland seizes in two years |
| Insulation resistance | Not measured after installation | At least 1 megohm at 500 V DC, then again at every annual stop |
The 1 megohm figure comes from IEC 60204-1 section 18.3, which is the electrical equipment of machines standard rather than a crane standard, and it is the number most commissioning sheets use. On a new machine in a dry hall we normally see hundreds of megohms. On a three year old pickling crane we have measured below 2 megohms with everything still working, which is the point at which the next wet season becomes a trip.
The other acid-specific item is the enclosure material, not the rating. IP66 in painted mild steel is not IP66 for long in hydrochloric acid mist. We specify stainless for the panel and the terminal boxes, and we accept that the stainless is the reason the electrical package costs more than the mechanical one on these machines.
Nothing about the electricity. A cleanroom crane is electrically ordinary: 400 V, a drive, a hoist, a pendant. What the room objects to is that the crane is a moving particle source, an ESD source and an EMI source, and none of those appear on a hazardous area specification at all.
The particle problem has a specific answer that surprises people. The obvious electrification choice, an open conductor bar, is the worst one, because a carbon collector shoe running on a copper bar wears and the wear product is fine conductive dust. It goes straight into the room. VAHLE, who build cleanroom electrification, market conductor bar, contactless power and cable-based systems specifically on reduced particle emission, ESD risk and EMI, which tells you the choice is not automatic and depends on the class.
The motor is the second source. A standard motor draws room air through itself for cooling and pushes it back out, carrying whatever it picked up inside. Cleanroom cranes use HEPA-filtered motor ventilation so that unfiltered room air never passes through the drive, and sealed stainless housings around motors, gearboxes and cable trays so lubricant and debris stay inside the equipment.
| Source | Mechanism | Fix |
|---|---|---|
| Collector wear | Carbon shoe on copper bar generates fine dust | Sealed system, cable festoon, or contactless transfer |
| Motor cooling air | Room air passes through the motor and returns | HEPA filtered ventilation, or duct the exhaust out of the room |
| Wheel and rail wear | Cast steel wheels shed oxide | Non-shedding polymer wheels and rails |
| Lubricant | Oil mist from bearings and brakes | Lubrication-free bearings, dry brakes |
| Track joints | Gaps trap and release dust on every pass | Gap-free joints, sealed and wipeable surfaces |
ESD is the other half and it is more dangerous than the particle count. A crane is a large isolated metal mass moving over a sensitive product. If it is not bonded, it charges, and it discharges into whatever is nearest. Cleanroom cranes use built-in grounding wires through the structure for exactly that reason, and the same 10 ohm target from the hazardous area section applies.
One thing to be clear about: a cleanroom crane is not an Ex crane and an Ex crane is not a cleanroom crane. We have been asked for both on the same machine exactly twice, in pharmaceutical plants handling solvent and powder in the same room. It is possible, and the electrical package becomes the largest single item on the quote.
Power and control are not the same circuit and on a special crane they rarely share a conductor. A conductor bar can carry power and nothing else, which is a limitation that catches people out on modular systems. On a hazardous area machine the same split appears for a different reason: the signal has to cross the same moving joint as the power, and on a rotating machine that means a slip ring with a separate ring stack.
The materials differ, which is the useful detail. On an Ex slip ring the power rings use copper-graphite brushes and the signal rings use silver-graphite, with phosphor bronze rings and precious metal plating for signals, and at least two brushes per ring. That is not decoration: silver-graphite gives a lower and more stable contact resistance, which is what a 24 V signal or a bus needs, while copper-graphite survives the current and the arcing of a motor circuit.
Where a bus is involved, the same slip ring can carry PROFINET, PROFIBUS or CAN, but the cable and the shielding become part of the certification package. Our rule is simple: if the control is anything other than hard-wired 24 V or a pendant, the signal path gets its own drawing, its own segregation distance from the motor cable, and its own test at commissioning. The alternative is a machine that runs perfectly in test and faults intermittently in production.
More than most people expect, and the number is set by the drive rather than the motor. IEC 61800-5-1 requires attention once the leakage current exceeds 3.5 mA for AC or 10 mA for DC, and at that point one of three things has to be true: the protective conductor is at least 10 square millimetres of copper, or there is a second protective conductor in parallel, or the earth conductor is monitored by something that trips on a fault.
The magnitude is predictable enough to estimate. A rule of thumb used by drive makers is 20 mA per drive plus 1 mA per metre of motor cable at 8 kHz switching frequency, and 2 mA per metre at 16 kHz. On a special crane the cable runs are long because the panel sits at one end and the hoist travels, so the cable term grows quickly.
| Case | Estimate | Consequence |
|---|---|---|
| One drive, 8 kHz, 40 m cable | 20 + 40 = about 60 mA | Over the limit. 10 mm squared PE or a second conductor |
| Three drives, 8 kHz, 25 m each | 60 + 75 = about 135 mA | A 30 mA RCD on the feeder will not hold, and should not be asked to |
| Same at 16 kHz | About 210 mA | Doubling the switching frequency doubles the cable term |
Two consequences follow, and both get argued about on site. The first is the residual current device. Only a type B device is permitted upstream of a drive, because the leakage has a DC component that a type A or AC device cannot see, and every device upstream of the type B one must also be type B. Retrofitting a type B RCD onto a feeder that already has a 300 mA type AC device is not a parts swap, it is a protection study.
The second is the earth conductor itself. A 10 square millimetre earth in a festoon cable is unusual and it is the reason some suppliers quietly fit a 6 square millimetre and hope. On a hazardous area machine that is not a shortcut, it is a finding at the audit.
These are our own planning figures from quotations, not a published statistic, and they move with the zone, the certification body and the market. They are percentages over our standard indoor crane electrical package for the same capacity and span.
| Room | Electrical package premium | Where the money goes |
|---|---|---|
| Dust, Zone 22, Category 3 | Plus 45 to 80 percent | IP6X enclosures, dust-rated motor, declared T-class, brake |
| Dust, Zone 21, Category 2 | Plus 70 to 130 percent | Certified enclosures everywhere, certified glands, project file |
| Gas, Zone 2, Category 3 | Plus 35 to 60 percent | Ex motor, ATEX festoon, no conductor bar |
| Gas, Zone 1, Category 2 | Plus 90 to 160 percent | Certified drive-motor combination, thermal protection, Ex collector |
| Pickling, acid | Plus 30 to 55 percent | Stainless everything, heaters, sheath upgrade, reel instead of bar |
| Cleanroom, ISO 7 | Plus 60 to 110 percent | Sealed drives, HEPA motor air, polymer wheels, no open bar |
| Cleanroom, ISO 5 | Plus 120 to 200 percent | Contactless transfer where class demands it, full stainless, validation |
The premium is not the expensive part. The expensive part is discovering the zone after the crane is on the water, because the retrofit is done at site rates with the crane shut down. We have quoted a Zone 1 conversion on a delivered machine at roughly the price of the electrical package itself, twice over.
These are from our own service records on special cranes, not a published study, and they are worth reading as a list of things that are easy to miss rather than as a ranking.
| Issue | Share | Prevention |
|---|---|---|
| Gland not Ex rated, sheath cracked at the gland | 24 percent | Gland schedule on the drawing, checked against the cable list |
| Rail bonding never measured, only installed | 18 percent | Record the ohms at commissioning, at every joint |
| Condensation heater failed or never wired | 16 percent | Heater on its own circuit with a visible indicator |
| Drive parameters left at standard motor defaults | 14 percent | Thermal model set to the class limit, and photographed at handover |
| Sheath attacked by acid mist at a low point | 12 percent | No low points. Drain loops and stainless tray |
| Particle count failed from festoon cable outgassing | 9 percent | Low-outgassing sheath specified, not assumed |
| Slip ring brushes not seated before load | 7 percent | Run in at no load, then check contact resistance per ring |
Only one of those seven is a component failure. Six are installation or documentation failures, and every one of them is invisible at the factory acceptance test and obvious at the first audit.
Ten items. If any of them is missing from the enquiry, the quotation will carry an assumption, and the assumption will be the cheap one.
| Item | What we need | Why it changes money |
|---|---|---|
| 1. Zone and category | Zone number and ATEX category, per area of the building | Moves the package by tens of percent |
| 2. Gas or dust group | IIA, IIB or IIC for gas. Dust ignition temperatures for dust | IIC hardware is not the same product line as IIB |
| 3. Temperature class | T-class or the governing dust surface limit | Decides motor frame and whether a standard brake is allowed |
| 4. Ambient and layer | Design ambient, and the expected dust layer in mm | A 55 C shed or a 5 mm layer re-rates everything |
| 5. Drive or direct-on-line | Whether speed control is required, and whether the motor is already certified with a drive | A tested combination can double the motor lead time |
| 6. Travel speed | Bridge and trolley speed in m/min | Above 1 m/s the ATEX festoon option disappears |
| 7. Rotation | Whether any part of the machine slews continuously | Adds a certified slip ring, not a standard one |
| 8. Control and bus | Pendant, radio, or PLC with a fieldbus | A conductor bar cannot carry it. This changes the whole scheme |
| 9. Earth and RCD arrangement | Existing protection upstream, and the site earth target | A type B device and 10 mm squared PE may be needed |
| 10. Documentation language | Which certificates the site will actually be asked for | Notified body work is a line item, not a courtesy |
If you can answer all ten, the electrical package is a quotation. If you can answer four, it is an estimate with four assumptions in it, and the assumptions will all be in our favour rather than yours.
We build these machines for all four rooms, and the electrical package is designed with the room rather than after it. If you want the supply side reviewed before the crane is specified, the special crane range lists what we build for grab, precast, pickling, cleanroom and Ex duty, and the hoist side is on the hoist and accessory page. Send the zone drawing with the enquiry and we will quote the electrical package as a separate line, which is the only way to see what the room is costing you.
No. The conductor bar is the one component that cannot be made acceptable by enclosure, because the open sliding contact is the ignition source and the standards do not accept a cover as protection for it in a classified atmosphere. Adding Ex boxes to a bar-fed crane leaves the bar itself as the finding, and it is the finding an inspector will write first. The bar has to come out and be replaced with festoon, a reel or a certified collector.
No. The motor certificate covers the motor. A drive changes the thermal picture because it can run the motor below its rated speed, where the shaft-mounted fan moves almost no air. For Ex eb the standard requires a combined heat run test with the specific drive. For Ex d and Ex ec there are alternatives, including a certified thermal protection function with sensors in the winding, but somebody has to choose the route and document it. A standard drive with default parameters on an Ex motor is a finding waiting to be written. The special crane order sheet carries a line for exactly this.
IP65 is the working minimum and IP66 is what we specify for anything within splash reach of the tank. The rating is the easy part. The parts that fail are the sheath material, which has to be polychloroprene or equivalent rather than PVC, the glands, which have to be stainless or they seize, and the condensation heater, which has to be on its own circuit and actually wired. A stainless IP66 box with a PVC cable and no heater will fill with condensate in the first cold season.
At commissioning, and then at every annual inspection, with the values written down. The standard's guidance is that a metal path above 10 ohms is an early indication of corrosion or a loose connection, so the trend matters more than the absolute number. We recommend measuring at each joint rather than end to end, because a good end-to-end reading can be carried by a bearing and hides the strap that has already failed.
Physically yes, and in practice we try to avoid it. A crane that travels from a Zone 2 area into an unclassified area carries its Ex rating with it, which is acceptable, but the reverse is not: a standard crane cannot enter the zone. Where a single machine has to cross a boundary, the whole machine takes the higher classification, and the electrical package is priced for the worst room it enters.
Category 3 is protected in normal operation, which means one fault is not considered. Category 2 is protected with one fault assumed, which means the design has to tolerate a single failure and still be safe. In practice the difference shows up as duplicate protection, different enclosure testing and a longer certification file. It is also the difference between a Zone 2 quote and a Zone 1 quote, and it is usually the largest single jump on the electrical line of any special crane quotation.
Related articles:
Special Crane Installation Guide: What Has to Be Right Before the First Lift, 0.5 to 50 Ton
Special Crane Standards: ATEX, IEC 60079 and Cleanroom Classification Compared
Special Crane Energy Consumption: What Four Specialised Machines Draw Over a Shift
Special Crane Carbon Footprint: Where the Emissions Sit on a Grab, Precast and Cleanroom Machine
Hoist Regenerative Power: What a 5 Tonne Hoist Sends Back Up the Cable, 0.125 to 100 Ton