NEC 225.30 - Transformer outside, two MCCs inside building

[wroggent]

I'm curious if the following hypothetical installation would violate article 225.30 of the NEC.:

1000kVA 480V transformer outside of building feeds two 600A MCCs inside of building. Each MCC has a main breaker.

Since the total load is less than 2000A I don't think it meets the requirements of 225.30(C) apply. This is a question mostly about terminology - I'm not sure if there are multiple feeders to the building because (1) the MCCs are feed from the same source, (2) only one feeder (it's not a service) supplies power to the transformer, (3) the transformer supplies power only to the MCCs in the building, and (4) the only power into the building is from that transformer.


I see two potential arguments that could be made:
(1) there are two feeders to the building because there are two seperate MCCs
(2) there is only one feeder that 'supplies power to the building' which is the transformer feeder because of the points listed above


Please let me know your opinion

 

[dpc]

Sounds like a violation. Does not seem to comply with the "six handle" rule unless the MCC main breakers are extremely close together. See 225.32.

 

[iceworm]

wrog -
My translation is there are two feeders to the building. However, does the installation qualify under 225.30.E? If so, it is fine.

dpc -
My translation of 225.32 is: each feeder must comply separately - and this one does.

wrog -
Additional design thoughts
Most of my clients with similar installations:

power requirements < 2400A @480A (2000KVA xfm)
multiple MCCs spread around the facility​

have a switchboard fed from the xfm primary with circuit breakers feeding the separate mccs.

Just an opinion based on my experience - all medium to heavy industrial

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[wroggent]

Thinking about it a little more I think the installation may qualify under 225.30(A)(6) so long as that provision isn't restricted to secondary selective networks as the Handbook commentary might lead one to believe - then again I'm not really sure as 225.30(A)(6) sounds like at least two transformers would be required (or some other source such as a generator, UPS, etc.). The disconnects aren't located as near as they could be to the entrance of the conductors into the building so a switching procedure would be needed to qualify under 225.32 exception 1 - this would then make the installation permissible under 225.30(E) I suppose.

 

[dpc]

I agree it could fall under 225.30(E), but that depends on the ownership and management of the building. I'd want to get it worked out with the AHJ ahead of time.

 

[iceworm]

I think the installation may qualify under 225.30(A)(6) ...

That would be a stretch. Is there any way you could explain this to an AHJ rep using a clear voice, looking them in the eye? That's generally my test (the RFT). From what you have described - I couldn't. Cause this looks like a plain old money issue - we don't want to spend money on a secondary switchgoard if we can get away not having one.

But that is a different issue than from the original - are two feeders to a building ok.

And yes, there are a few other issues. Here are a couple:

Transformer secondary tap rules
As you noted - disconnects located nearest point of entrance. Apparently they aren't.​

Curiousity question:
Is this a new installation - ie. one being built or designed as we type? Or has this been in service for a while.

As for this being a money issue, that's okay. My clients are in favor of the most cost effective design available - I am as well. But that does not mean minimum installation money and code minimums. The jobs have to meet customer spec, be reliable, be safe to operate, meet code minimums. The first three are good design. The last is a legal issue and don't have a lot to do with the first three.

So where am I going?
If this is existing, in service, and you are looking for justification for not changing that is one thing.
If this is new construction, I couldn't pass the "Red Faced Test"

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[wroggent]

iceworm,

The design is crap (in more ways than what has been discussed) - there's no debate on that and it was certainly done this way because of money. The design isn't mine, but I am responsible for helping to fix it if need be. To be honest, I don't know exactly what 225.30(A)(6) covers and what it doesn't - I wouldn't try to tell the AHJ that the installation is covered by it but I would tell the AHJ that there are two MCCs and not one for redundancy purposes - whether that qualifies is up to them.

If by transformer secondary tap rules you're referring to distance and placement of overcurrent protection and cable sizes, I don't think that's an issue in this case - there's about 25 ft. or so of distance but it's an industrial installation anyway (and I think all of 240.92(C) is satisfied).

This particular piece of the facility is about 10 to 15 years old (i.e. it passed inspection, if there was one).

City fire chief says the adjacent facility is it's own AHJ (they have their own emergency response) - unfortunately I believe the adjacent facility is our AHJ as well (joint venture and same property). It's unfortunate because I believe they are the one's responsible for the design and the one's who would be paying to fix it. (conflict of interest?)

 

[iceworm]

The design is crap (in more ways than what has been discussed) - there's no debate on that and it was certainly done this way because of money. The design isn't mine, but I am responsible for helping to fix it if need be.

Ya got to love it - yes been there. And that part is okay - that's why they pay

I don't know exactly what 225.30(A)(6) covers.

Unless the two mccs supply redundant equipment - it does not apply. (JmO)

This particular piece of the facility is about 10 to 15 years old (i.e. it passed inspection, if there was one).

City fire chief says the adjacent facility is it's own AHJ (they have their own emergency response) - unfortunately I believe the adjacent facility is our AHJ as well

So who/what is driving the need to analyze the regulatory issues with the install?

Generally, once the equipment is installed and running, it is no longer an NEC issue. Might be an osha issue if someone can validate a safety issue. Although, could be an NEC issue if the AHJ says it was never installed per code in the first place. Ususlly for that to happen, the AHJ is in looking at something else and just happens to notice this one. (Or someone dropped a dime)

I'd be okay with telling whoever (whomever?) "Installation meets 225.30.E. A "documented safe switching procedure is required." Then you get to say, "Here it is." Or, "I've informed our management it is required."

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[wroggent]

Unless the two mccs supply redundant equipment - it does not apply. (JmO)

One is for "A" pumps and one is for "B" pumps. Is this what you mean?

The jobs have to meet customer spec, be reliable, be safe to operate, meet code minimums. The first three are good design. The last is a legal issue and don't have a lot to do with the first three.

So who/what is driving the need to analyze the regulatory issues with the install?

Me.

I've always looked at code violations as potential safety issues - aside from lobbying by electrical contractors and equipment manufacturers, why else would something be required by code? Maybe this is a dumb idea though.

Beyond that though we are modifying the installation - currently those MCCs actually are fed from a 500kVA transformer. A project is underway which involves increasing the load on the MCCs such that a 1000kVA transformer is needed. Unfortunately I did not recognize this (potential) issue until recently, but the project is already pretty far along.

 

[iceworm]

One is for "A" pumps and one is for "B" pumps. Is this what you mean?

'A' pump can be taken off-line and repaired while runnimg on 'B' pump? Close enough. 225.30.A.6 works.

So who/what is driving the need to analyze the regulatory issues with the install?

Me.

Best way to do it. You get to decide when you have gone far enough.

... I've always looked at code violations as potential safety issues - aside from lobbying by electrical contractors and equipment manufacturers, why else would something be required by code? Maybe this is a dumb idea though. ...

Not dumb. Probably an excellent way to approach.

Code is minimums. If you haven't, read 90.1.A, B, C. NEC is 'Practical safeguarding, essentially free from hazard, not necessarily efficient, convenient, or adequate', and I'll add 'reliable'. And it is not a design guide.

Yes, one must meet code minimums. And, the install should work, but it is dead marginal.

Still, I am usually more interested in what the code is trying to accomplish - moreso that a striclly legal interpretation of THE BOOK. Caution - there are AHJs that have disagreed with this - occasionally with near violence.

I believe the adjacent facility is our AHJ as well

Yeah that can be a problem - especailly if the owner can not see past the quarterly profits. Minimal interest in maintainability or even reliability.

... A project is underway which involves increasing the load on the MCCs such that a 1000kVA transformer is needed. Unfortunately I did not recognize this (potential) issue until recently, but the project is already pretty far along.

I'd say your work is done.

You can show the install meets code minimums - twice. That is all your customer is interested in. Unless you can show it is unsafe or illegal, your customer does not want to go back and change (shudder - money).

ice

Harmless flakes working together can unleash an avalanche of destruction