Feed thru lugs question

[GaTech04]

A project I am working on has a 400A MLO panel (208/120) and I need to add a second section. Is it ok to add feed thru lugs to feed a 225A MCB panel to be located right next to the 400A MLO?

There is about 12" of space at the bottom of the panel, which should suffice for the added lugs and the 4" min wire-bending space for the 1 set of #4/0s needed to feed the MCB of the new 225A panel.

I just want to make sure Im not overlooking anything that may violate code - thanks all.

 

[augie47]

Are you feed thru lugs part of a manufactured supplied kit or just lugs you are adding ?
That would be the only question I could see. By NEC your plan is basically sound, but if the lug kit is not "factory" you would be altering a UL listed panel and thus a violation..

 

[GaTech04]

We would buy the feed-thru lug kit from the factory (SqD).

We actually have the new 225A MCB panel left over from a different project and I was just hoping to use it to both free up space in the warehouse and save us from buying another 400MLO panel for the second section.

Thank you for the fast reply and glad to be a member of the forum.

GT

 

[Mike01]

Tap Rule??

Tap Rule??

One question you have a 400A mlo panel and you will be attaching lugs to the bus of the panel and taking #4/0 conductors to feed the 225AMCB panelboard? I am not sure but maybe someone elese can chime in sounds to me like the tap rule would be in effect here, because you have your 4/0 wire that is un-protected because the protection for it would be the 400A main to the 400Amlo panel, so as long as the new panel has a mcb (looking at your post it does) as long as you comply with the tap rules I believe you would be ok.

 

[GaTech04]

I think I see what you are saying -

Currently we have a 175/3P breaker in our 480/277 panel feeding a 112.5kVa Xfmr which feeds the 400A MLO 208Y/120. So the OCP for the 400A MLO is actually the breaker in the 480V panel.

I'll have to refresh myself on the tap rules since I havent really gone over them since I took my licensing test a little over a year ago. Basically for feeder taps Id have to make sure the following is true as long as the conductors arent over 10' correct?:

1) ampacity of the conductor is not less than the computed loads and not less than the device rating supplied (225A - #4/0 - check)
2) tap conductors dont leave the panelboards - check
3) enclosed in raceway/panels - check
4) line rating not more than 10x the rating of the tap conductor - check

Does that cover it all? If necessary I wouldnt mind using parallel #3/0 just to satisfy the 400A rating on the lugs - it looks like that shouldnt be necessary though (still alot less expensive than buying a new panel though)

Thanks again!

 

[augie47]

correct, tap rules would apply, but the OP stated "right next to" so I didn't mention them, but, as you stated, 240.21 would have to be taken into account.

 

[jim dungar]

I think I see what you are saying -

Currently we have a 175/3P breaker in our 480/277 panel feeding a 112.5kVa Xfmr which feeds the 400A MLO 208Y/120. So the OCP for the 400A MLO is actually the breaker in the 480V panel.

I'll have to refresh myself on the tap rules since I havent really gone over them since I took my licensing test a little over a year ago.

The primary breaker of a multi-voltage transfromer cannot protect the conductors on the secondary of the transformer. With your 208Y/120V the secondary conductors are already considered taps.

You need to reading 240.21(C).

 

[augie47]

As Mike pointed out, you would need to keep 240.21 (Tap rules) into account. As you stated "next to", I assumed you would be in compliance.

More importantly, now that you have provided more detail, as Jim pointed out, it appears that your original install is not NEC compliant. 240.21(C)(1) in particular and the FPN 1 to 450.3 have not been addressed.

 

[infinity]

Actually your #4/0's would fall under the 25' tap rule not the 10' since their ampacity is 1/3 or larger than the 400 amp OCPD ahead of the tap.

 

[GaTech04]

OK I think Im getting more confused now.

Im looking at 450.3 and it refers me to Table 450.3 (B) since the transformer is under 600V. Would I not be able to use the "Primary Protection only" row which would only require the primary protection of 125% of the current?

112.5k / (480 x 1.73) = 135.5 x 1.25 = 170 which moves up to 175A breaker per note 1

I apologize in advance for any thickheaded misinterpretations Im having.

EDIT - I think I see my error - That is for a Delta-Delta transformer, and I have a Wye-Wye, which is not considered to be protected by the primary OCPD

So it looks like my solution would be to buy a new 400A MCB panel with feed thru lugs to feed the existing MLO I have on site.

 

[GaTech04]

Doh - meant I have Delta-Wye.

And I just found a 400A MCB Square D panel in the warehouse as well, so this should work out just as well if that is the only error you guys see.

Thank you!

 

[augie47]

OK I think Im getting more confused now.

Im looking at 450.3 and it refers me to Table 450.3 (B) since the transformer is under 600V. Would I not be able to use the "Primary Protection only" row which would only require the primary protection of 125% of the current?

112.5k / (480 x 1.73) = 135.5 x 1.25 = 170 which moves up to 175A breaker per note 1

I apologize in advance for any thickheaded misinterpretations Im having.

EDIT - I think I see my error - That is for a Delta-Delta transformer, and I have a Wye-Wye, which is not considered to be protected by the primary OCPD

So it looks like my solution would be to buy a new 400A MCB panel with feed thru lugs to feed the existing MLO I have on site.

Exactly correct... and welcome to the Forum.

 

[raider1]

Also take a look at 408.36(B) (2008) or 408.36(D) (2005).

The overcurrent protective device for a panelboard fed from a transformer must be installed on the secondary side of the transformer.

Chris

 

[RUWired]

While were checking, what size conductors are feeding the 400 amp main breaker from the secondary side of the transformer.

Rick

 

[Pierre C Belarge]

Have you performed a load calculation to see if the additional load does not exceed the permitted load?

 

[Mike01]

Just for kicks..

Just for kicks..

The concern would be because of the fact if you are landing in a 400A MCB from the 112.5Kva xfmr. The conductors have to be sized to match the OCPD they are landing in so 500mcm conductors would not work for this installation you would either need to use 600?s (there are other inherent problems with using 600?s like making sure you can fit them on the breaker and maintain your wire bending space, and making sure the lugs on the breaker except 600?s) or you could run parallel 4/0?s to the 400AMCB most will accommodate this but don?t forget to size your ground per 250.66 not 250.122. there are some circumstances where you are not required to have a single over current protection on the secondary but they are limited applications and sound like they do not apply here.

 

[GaTech04]

I believe we used 2 - sets of #3/0 with a #3 ground in each from the secondary of the transformer to the 400A panel. We will have to redo this soon though to switch in the 400A MCB - so if I need to raise that to #4/0 with a #2 ground it would be a small matter. I definately do want to do it correctly.

I did the load calc's myself and came up with right at 105 kVa (~290A). This was using nameplate data on alot of the gym equipment (treadmills etc) and going a little high on things I didnt have enough information on.

Here is a pic of the summaries - thanks for looking over them.

Thanks again.

 

[GaTech04]

To clarify -

I did the load calculations and power/lighting layout for this tenant buildout, basing the loads on the equipment he is currently using in his existing facility. This was mainly for my estimating purposes, and we are going to forward all of my work to an engineer to develop stamped drawings to do the install from. He should catch any errors that Ive made before the actual install.

The tenant build out is actually the second phase of the project, the first phase we split a tenant space (built a demising wall) and added the new service (400A 480/277 + the 112.5 kVa and the 400A 208/120 panels). The service is done, but we are having to modify to accomodate the new tenant.

 

[GaTech04]

or you could run parallel 4/0?s to the 400AMCB most will accommodate this

Wouldn't #3/0 THHN work since wire and terminations are 75deg+?

 

[Mike01]

brain fart.

brain fart.

3/0 would be fine to me