Control Cabinet Regulations

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Thread Starter

wwlederer

Our small company produces a special technology equipment (consists of pumps, motors, PLC, etc.) for general industrial use. I design the control cabinet. Which regulation documents must I follow for electrical installation inside the cabinet? The UK (EU) law is particularly interesting.

Another question: if we use 240V AC, do we have to install a general isolator into the control cabinet?

Thank You,

Wal
 
There isn't just one regulation regarding control cabinets. In fact there are many.

NEMA
1. There are some requirements regarding the cabinet's ability to protect against the elements such as dirt.

NEC
1. Cabinet's metal structure should be grounded for personal protection.
2. Control signals wiring should not have mixed voltages in the same raceway.
3. Power distribution cables should be properly sized and coordinated so that damage by electrical faults are minimized.
4. Cabinets opening must have a minimum of 3 feet of clearance.

IEEE
1. Ground cables should be either bare conductor or have green insulation.
2. Each cabinet should have its own ground path to the earthing triad. There should not be more than one ohm of resistance between cabinet and ground grid or triad.

And then there is engineering common sense:
1. Heavy power supplies are installed at the bottom of the cabinet for stability.
2. All cabinets in the same row should have doors swing in the same directions and (hopefully same exterior color)
3. Any MMI panels should be at eye-level.
4. There should be enough cooling to dissipate heat at a certain ambien temperature.
5. Cabinets being complexed together must be able to fit thru the opening of the equipment room.

There are rules I remember off the top of my head.

There are many more, some of them come from customer's specific requirements.

Tom Tran
www.industran.com
 
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marc sinclair

Hi,

The UK has been part of Europe for some time now. :) Products destined for sale or operation in the UK are subject to European law. This has been
greatly simplified with the introduction of CE marking and harmonised standards. If you wish to self-certify your equipment, you will need to research and comply with any of the relevant harmonised standards. When you are satisfied that you do, then you must create a certificate (either
a certificate of conformance if the machine is a stand alone unit, or of incorporation if the machine will integrate into other equipment) and affix a CE mark. You should also create a technical construction file (your working-out:) which should be available for inspection if a query arises.

All the relevant information is freely available on the 'net including the majority of the regulations and directives. If in doubt, get help from someone who has been through the process.

Marc Sinclair
www.germainesystems.eu
 
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Bob Peterson

> There isn't just one regulation regarding control cabinets. In fact there
are many.
>
> NEMA
1. There are some requirements regarding the cabinet's ability to protect
against the elements such as dirt. <

[comment] NEMA standards are not enforcable. They are product standards.

> NEC
...
2. Control signals wiring should not have mixed voltages in the same
raceway. <

[comment] Totally false, and has nothing to do with the inside of a control
cabinet in any case, as the NEC only applies to premises wiring, and control
cabinets are not premises wiring.
>
> IEEE
[comment] IEEE standards are not enforceable.
>
> 1. Ground cables should be either bare conductor or have green insulation. <

[comment] NEC/NFPA79/UL applies to color coding of ground and bond wires.

> 2. Each cabinet should have its own ground path to the earthing triad.
There should not be more than one ohm of resistance between cabinet and
ground grid or triad. <

[comment] Nonsense. There is no enforcable US specification for the
resistance of bonding and grounding wires that says one Ohm. One Ohm may
well be too high. The impedence of the bonding conductor is only required to
be a minimum size based on the OCPD sizing and the requirement that the OCPD
must see enough current to trip if a ground fault occurs. Normally this is
5-6X the rating of the OCPD, so on a 120V circuit, with a 20A circuit
breaker, the bonding impedance would need to be about 1 Ohm, and cannot be
less then #12 in any case. Figure out how much wire it would take to get one
ohm of impence in the ground fault path (remember both directions) and that
will tell you the maxium length of #12 you can run and have the OCPD trip
reliably. If it won't trip reliably with #12, you must increase the size of
the wire until it will reliably trip.

> And then there is engineering common sense:
1. Heavy power supplies are installed at the bottom of the cabinet for
stability. <

[comment] or you could put them at the top so the heat generated does not
adversely affect other components. :)
 
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Bruce Axtell

In the U.S., NFPA 79 (formerly the JIC standard) is one standard that governs control enclosures.

Bruce A.
 
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Steve Barcik, HTDS.LLC

Hello,

I provide ongoing support to electrical designs for achieving conformance with many regulations; your specific design would need to conform to NFPA 79 as a base and to others like as NFPA 70 and more for the USA and to other codes for Europe and Asia, other standard do apply.

Drop me a line or call if you have specific questions.

Steve Barcik
512-963-0222
 
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