Tansformer Code Clearance

[norval g. dixon sr]

I have a panelboard 3'-0" away from a 75KVA transformer that is facing it that was installed by an electrical contractor.
The Electrical Inspector in the state of Michigan has state that in section 110.26(A) of the 2002 NEC, this transformer falls under condition 3 that requies a 4' clearance. The inspector has stated that these two peices of equipment could be subjected to live parts. Does this really apply for a transformer clearance.

 

[George Stolz]

I believe the inspector is correct. If the two are facing each other, then you can have a live panel behind you, and a live transformer in front of you. Therefore, it falls under condition 3, and provided one of them is greater than 150V to ground (which is presumably the case), then you need 4 ft of depth of working space.

 

[bphgravity]

I agree with George. 8)

 

[rbalex]

I find myself in the uncomfortable position of disagreeing with both George and Bryan. What ?could? happen is a far cry from what ?is likely? to happen and an even further cry from what is "likely to [be] require[d]."

Unless the transformer and panel are functionally associated, it is difficult to describe a scenario (one that isn?t manufactured, that is) that would require the simultaneous ??examination, adjustment, servicing or maintenance while energized?? of both items of equipment.

Nevertheless, assuming the transformer case is grounded, it is still clearly Condition 2 and a 3? depth is non-compliant..

 

[George Stolz]

I don't know about that line of reasoning.

I see it as:

• Will the panelboard likely require servicing while energized (as far as the NEC is concerned)? Yes.
• Will the transformer require servicing while energized? Yes.

There is not really an exception or other language where you're allowed to consider that it's not likely to transpire at the same time. If it's possible, then it is so, IMO.

 

[rbalex]

But will there be exposed live parts on both sides? See the definition of Condition 3?

This was a MAJOR issue for the 70E TC when CMP1 casually accepted the new definition of live parts in the 2002 Code without thinking through all its implications. This is one of the reasons the "Conditions" were redefined in 2005.

 

[don_resqcapt19]

Bob,
Look at 110.26(A)(1)(c). This has been in the code for a number of cycles. This words says to me, that equipment that normally has its covers on or closed, and facing each other is intented to be a Condition 3 installation. This wording first appeared as Exception #3 to 110-16(a) in the 1996 code.
Don

 

[George Stolz]

I've been studying this for a bit. (Doesn't everybody sit on the computer all vacation?)

Is the "wood" referred to in the 2002 cycle a permanent barrier, or a barrier installed while work is in progress?

I agree with Don's view, and it tickles me that I've been sitting here looking at this with such scrutiny and didn't think to look further for more context, as he did.

 

[rbalex]

I was part of the IEEE Safety Subcommittee that proposed the 1996 Exception. The problem is that Live Parts keep getting redefined.

Prior to the 2002 NEC, Live Parts was defined as "Electric conductors, buses, terminals, or components that are uninsulated or exposed and a shock hazard exists." The assumption was that metal enclosed equipment facing each other were considered to be Condition 2 since it was presumed no shock hazard existed from the gear "across the aisle? ? even if it were open. However, the problem arose earlier (can?t remember which edition) when the measurement requirements were specified as from the live parts, if exposed, or the cover if enclosed.

If equipment was upgraded many existing installations instantly became non-compliant-so the exception was generated.

The condition became worse from a practical standpoint when ?Live Parts? was redefined to its current definition: ?Energized conductive components.?

So several tweakings of the ?Condition 3? have occurred, primarily to recognize that what may be ?across the aisle? can be temporarily guarded while working on live equipment (making it Condition 1) or, as is now the case, in 2005 the ?live parts? must actually be exposed on both sides to require Condition 3. The ?guarding? proviso has been eliminated, so it will be a Condition 2 as a minimum; but the literal requirement of Condition 3 is that there must be exposed live parts on both sides. This has been the 70E TC fallback for some time now.

I?m going to be very interested in what happens to 110.26 in the next cycle. In truth, there is no inherent increase in fire or even shock hazard introduced by the installation itself for deadfront equipment ? no matter what the spacing is. There is obviously a worker safety issue though. The 70E TC and CMP1 have been at odds over this for some time.

 

[don_resqcapt19]

Bob,

So several tweakings of the ?Condition 3? have occurred, primarily to recognize that what may be ?across the aisle? can be temporarily guarded while working on live equipment (making it Condition 1) or, as is now the case, in 2005 the ?live parts? must actually be exposed on both sides to require Condition 3.

If that is the case, then why is 110.26(A)(1)(c) still in the code?

(c) Existing Buildings. In existing buildings where electrical equipment is being replaced, Condition 2 working clearance shall be permitted between dead-front switchboards, panelboards, or motor control centers located across the aisle from each other where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the aisle from being open at the same time and qualified persons who are authorized will service the installation.

That still says that the panel believes that dead front is the same as exposed live parts.
Don

 

[rbalex]

Actually its fairly clear that the exception assumes one side of the workspace is a deadfront. Now, I can only point to the current literal verbiage of Condition 3.

As I said, I'm going to be interested in what happens this time around. This Section seems to be in constant transition. Where we are now has been caused by a series of unintended consequences.

Remember, the larger philosophical bent of the 70E TC, at least during the time I was on it, is that you shouldn't do live work at all. (Although this was certainly not by a wide majority.) If you do live work it is supposed to be "by necessity" only-and continued production alone isn't considered to be a sufficient necessity. I can readily design an industrial distribution system that rarely, if ever, needs a worker to "work live" and can still maintain continuous production. It certainly has a higher installed cost - but it also has the side benefit of being far more reliable, often by 2-3 orders of magnitude.

I cannot speak for either TC of course - but there seems to be a definite line drawn between those who don't want any live work and those who want to do live work "safely." Both sides have fairly large voices on both TCs.