Electrical machine and removable panels bonding

[patm72]

Hello,

I have a machine in an enclosure with multiple doors and bolted panels. The machine itself has a 25A three-phase 480VAC fused disconnect, for driving two motors of respectively 1 and 5 HP. At the core of the machine is a gas turbine.

I'm actually pushing for having all doors and bolted panels bonded to the frame, which is to be grounded. IMO, they all should be, despite not having any electrical component mounted on them per se.

I have seen a few threads referring to judgment calls on this topic, but the very nature of the thing (gas lines inside) should vouch for the bonding.

Am I right in my assertion?

Thank you.

 

[waross]

When cabinet doors have components mounted in/on them, a grounding jumper to the door is common.
The hinges are not depended upon to maintain electrical continuity over time.
Anything electrical, pilot lights, push buttons, switches, may justify a grounding jumper to the door.
The size?
The size of the grounding jumper is determined by the largest breaker or fuse holder for circuits feeding the door mounted equipment and the appropriate code section.
Without a bonding jumper, and with corrosion over time compromising the electrical continuity of the hinges, the door itself may become a shock hazard in the event that a wire comes off of a terminal and grounds out.
Never seen that happen? Wait for it.
The first time I saw it, was not a door but the wire grounded inside the control cabonet.
THis was about 50 years ago in what was at the time one of the highest producing sawmills in the Pacific Northwest and at the time, the most automated.
Management accepted about 20 minutes of down time per shift, and after that counted the cost of downtime at $50 per minute.
That one wire grounded out shorted out the control scheme and brought the entire mill to a stop.
Vibration, just opening and closing the door, wire can and do work loose. Plan for it.
Hint: If you want to justify grounding the doors, mount a pilot light or some electrical component on the door and you have your justification.



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr. patm72 (Electrical)(OP)19 Sep 23 15:34
"...I have a machine in an enclosure with multiple doors and bolted panels....I'm actually pushing for having all doors and bolted panels bonded to the frame, which is to be grounded. IMO, they all should be, despite not having any electrical component mounted on them per se...".
You had very knowledgeable and valuable advice already.
I wish to add a little information on this subject: In US reference to NEC Art 250. Personal opinion/additional information.
1. All doors which are hinged onto the frame with/without equipment on it, shall be bonded to earth. Attention: a) connection devices or fitting that depend solely on solder shall not be used. b) sheet metal screws shall not be used to connect grounding concoctor to encloser.
2. All removeable bolted panels (without any electrical components mounted on them) are usually "not practical" to have additional specific bonding connection to the earthed frame. In this case, the low contact resistance through the mounting metallic screws are considered adequate. For "practical" reasons, it is considered cumbersome to remove the bonding connection on a removable panel without any equipment on it.
Che Kuan Yau (Singapore)

 

[waross]

Thank you for the clear reference, Mr Che.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!