Enclosure requirements

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dvang

Member
(2) Questions involving electrical enclosure.

-1. NEC 312.6.C requires that 4 awg or larger cable(s) to be installed per NEC 300.4.G. (In other words, include a bushing at the cable entry point). My question is: can the bushing/enclosure structure be viewed as a supporting structure?

-2. Does NEC have requirements regarding electrical devices mounted (internally) at ceiliing? This device is a 2 ohm "resistor" used to discharge extra amount of currents (50A). The device will be online for 5 mins at the max. And ofcourse we'll provide adequete standoffs & insulations.

Thanks in Advance.
 

benaround

Senior Member
Location
Arizona
(2) Questions involving electrical enclosure.

-1. NEC 312.6.C requires that 4 awg or larger cable(s) to be installed per NEC 300.4.G. (In other words, include a bushing at the cable entry point). My question is: can the bushing/enclosure structure be viewed as a supporting structure?

-2. Does NEC have requirements regarding electrical devices mounted (internally) at ceiliing? This device is a 2 ohm "resistor" used to discharge extra amount of currents (50A). The device will be online for 5 mins at the max. And ofcourse we'll provide adequete standoffs & insulations.

Thanks in Advance.

A bushing is just a plastic threaded fitting that screws on to the pipe or connector and

has no supporting value.

-2. ?
 

dvang

Member
Question 2 calarified.

Question 2 calarified.

For qestion 1.
For conduit runs, from point of entry of enclosure to the next 3m run; there shall be a support. That is why i would consider the bushing as a support.

For question 2.
In other words. Typical enclosures have light fixtures screwed onto the underside of the enclosure, my question relates to having "powered" components be installed in the same location. NEC require me to have a air gap of 0.5" (208V component) as specified in 312.10 for back, walls & metal partition. Nothing is said regarding enclosure ceiling.

For me this is confusing, however I think I answered my own question. As long there is a 0.5" gap for 250V or less, I should be fine.
 

juptonstone

Member
Location
Lady Lake, FL
bushing as support

bushing as support

The bushing can not be a support, however the enclosure where the conduit enters can be a supporting means. I assume that there is a TA or Male/Terminal Adapter on the end of the conduit, with a lock nut... which fits securely in a hole in the enclosure. If the enclosure is secured, then the conduit is supported at that point.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
For qestion 1.
For conduit runs, from point of entry of enclosure to the next 3m run; there shall be a support. That is why i would consider the bushing as a support.

Can you explain what this means?
 

dvang

Member
Pardon my speel, I should not quote the NEC code book from memory.

Per NEC, 344.30 (B), conduits shall be supported at intervals not exceeding 3m (10ft).
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Pardon my speel, I should not quote the NEC code book from memory.

Per NEC, 344.30 (B), conduits shall be supported at intervals not exceeding 3m (10ft).
Yes, the conduits must be supported, but in general the conduit termination is not a support for the conduit.
 

dvang

Member
Another hicup

Another hicup

Item 2. is a 2 ohm resistor dissapating 1600W :)O).

It now seems that the placement of item 2 isn't critical since its not install inside the panel. Its new location is externally at the top & SRML cables will be wired from the panels side with appropiate fittings to the resistor.

Note: SRML = Silicone Rubber Motor Leads, otherwised know as SA cables. There were some forum queries regarding this cable type.

The current issue is "wiring/piping conduit to it". In NEC, I didn't see a requirement for conduit runs (flex or rigid) if I wired the cable from the side of the panel (near the top) to the resistor (at the top). It only requires approved fittings.

Knowing that conduit is only meant to protect "non-armoured" cables from being knicked & banged up. I don't think it's necessary since this resistor is not placed in servicing area. BTW this is an indoor istallation, if it was outdoor I would defintely use conduit.

-dvang
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Item 2. is a 2 ohm resistor dissapating 1600W :)O).

It now seems that the placement of item 2 isn't critical since its not install inside the panel. Its new location is externally at the top & SRML cables will be wired from the panels side with appropiate fittings to the resistor.

Note: SRML = Silicone Rubber Motor Leads, otherwised know as SA cables. There were some forum queries regarding this cable type.

The current issue is "wiring/piping conduit to it". In NEC, I didn't see a requirement for conduit runs (flex or rigid) if I wired the cable from the side of the panel (near the top) to the resistor (at the top). It only requires approved fittings.

Knowing that conduit is only meant to protect "non-armoured" cables from being knicked & banged up. I don't think it's necessary since this resistor is not placed in servicing area. BTW this is an indoor istallation, if it was outdoor I would defintely use conduit.

-dvang
In general the NEC does not permit open wiring. It must be in a Chapter 3 wiring method. Chapter 3 includes raceways as well as cables. Type SA conductors are listed in Table 310.13 so they will have to be installed in a raceway of some type.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am inclined to agree. Just how would you support such an installation?

A Unistrut framework would be ugly and serve no real purpose.

I have such an issue I am currently trying to deal with and have not come up with any answers I like.
 

dvang

Member
Nec 344.30(a) & (b)

Nec 344.30(a) & (b)

NEC defined two vocab: "support" & "fastend". I think we need to get the verbiage correct first and then we can answer the question properly.

Per NEC 344.30(A).
RMC shall be securely fastened within 900 mm (3ft of each outlet box, junction box, device box, cabinet, conduit boy, or other conduit termination. Fastening shall be permitted to be increased to a distance of 1.5m (5ft) where structural members do not readily permit fastening within 900mm (3ft).

Per NEC 344.30(B).
Conduit shall be supported at intervals not exceeding 3m (10ft).

Correct me if I'm wrong; 344.30(A)/(B) does not say that a conduit hub is or is not a support. Part (A) It only states that RMC exiting an enclosure needs to be secured within 3ft. (Secured not supported)
Part (b) answers "petersonra's" question. It would be acceptable as long as it's under 10ft for 0.5-0.75 trade size.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The hub is the conduit termination and the raceway must be securely fastened within 3' of the conduit termination. If CMP8 considered the conduit termination to be a support they would not have made the change in the 2008 code to permit a nipple of 18" or less to be supported only by the conduit terminations.
 

dvang

Member
Oh on the contrary.

Oh on the contrary.

In general the NEC does not permit open wiring. It must be in a Chapter 3 wiring method. Chapter 3 includes raceways as well as cables. Type SA conductors are listed in Table 310.13 so they will have to be installed in a raceway of some type.

A cable with a TC-ER (Tray Cable - Exposed Run) marking is allowed to be run "exposed" by the following method described in NEC.

2008 National Electrical Code? Excerpt Type TC Cables Article 336.10 (7) In industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons service the installation and where the cable is continuously supported and protected against physical damage using mechanical protection, such as struts, angles or channel, Type TC tray cable that complies with the crush and impact requirements of Type MC cable and is identified for such use with the marking Type TC-ER shall be permitted between a cable tray and the utilization equipment or device. The cable shall be secured at intervals not exceeding 1.8m (6ft). Equipment grounding for the utilization equipment shall be provided by an equipment grounding conductor within the cable.

Nevertheless, I would still need to run my 12 awg SRML cables in conduits. :)
 
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