Dry-Type Transformer Enclosures

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meby's picture
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Joined: 2012-04-17

The 2014 Edition of the NEC now requires a terminal bar be secured inside the transformer enclosure for all bonding and grounding conductor connections. What effect will this have on your installation practices? Will it save you any time or money?

skd76's picture
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Joined: 2013-09-11

Logical requirement. It is cetrtainly possible to install open lugs on the bottom or sidewall of the xfmr. It is often done poorly. Hope is that the xfmr mfr will step up and provide a bar (similar to an intersystem bond bar - but larger) in the xfmr. Intermediate fix will be to install at time of xfmr wiring with an aftermarket device.
Mr. Eby, may I suggest that when one throws a new or little-known Code rule out for discussion, that they include the section number"(s) as a part of the topic question? Perhaps that should be in the What you need to know...Read-me-1st postings"? Or as a flyer on the "New Topic" initial post page?
New forum tool is quite welcomed! Thanks.

meby's picture
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Joined: 2012-04-17

Hi, skd76. Thanks for your response to my post.

Your suggestion to include the actual Code reference in my original post makes perfect sense. I typically do so, but obviously missed the mark this time around. This new requirement can be found in Section 450.10 of the 2014 NEC.

Your suggestion to add this tip to our rules list is a great idea. I'll pass that along to our Forum Administrator.

I'm also happy to hear you like the new forum on our site.

Regards,
Mike

Joanie's picture
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Joined: 2015-05-27

Lately, some of our engineers have tried to establish a design rule that a pad-mounted transformer require a ground rod at each corner and connection by a 2/0 ground wire, creating a ground loop around the transformer. I do not believe this is necessary. I also believe that it has the effect of transferring the single point ground for the facility from the service entrance location (a ground rod outside) to the transformer, no matter how far away.

What are your thoughts?

Thank you!

Pipeandwire's picture
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Joined: 2016-10-07

Hello. I have a general question to solve a discussion regarding transformer grounding and bonding.

480V Delta primary to 120/208V Wye secondary.
With the exception of the terminal block stuff, etc, I'm saying the main bonding jumper can be at the transformer bonding cold water or building steel with Xo, ground to panel and transformer case (I realize it can also be at 1st point of disconnect). The question is do we need a secondary bonding at neutral bar to ground? I say no, it's not required.

Second question. My brother is stating the panel needs a separate ground brought in to the ground bar. I say no this is not required. A ground has already been established and don't want to cause a loop.

Can anyone please clarify for us?
Thank you.

Paul Abernathy's picture
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Joined: 2012-12-21

[quote=Pipeandwire]Hello. I have a general question to solve a discussion regarding transformer grounding and bonding.

480V Delta primary to 120/208V Wye secondary.
With the exception of the terminal block stuff, etc, I'm saying the main bonding jumper can be at the transformer bonding cold water or building steel with Xo, ground to panel and transformer case (I realize it can also be at 1st point of disconnect). The question is do we need a secondary bonding at neutral bar to ground? I say no, it's not required.

Second question. My brother is stating the panel needs a separate ground brought in to the ground bar. I say no this is not required. A ground has already been established and don't want to cause a loop.

Can anyone please clarify for us?
Thank you.[/quote]

Greetings Pipeandwire,

I need to reconstruct your question in order to make better sense of what you are asking. The SBJ (System Bonding Jumper) is designed to be typically at the XFMR or first disconnection means and generally not both locations, with of course some acceptable applications as expressed in the NEC to which it could be both locations where applicable. However, it usually only takes place at one of the two locations. If that happens to be at the first disconnection means then we have an SSBJ from the grounded point to that first disconnection means.

The connection to the water pipe or building steel as you referring to is totally different. That is the connection that is required per Sec. 250.28(A)(5) and (6) respectively. That connection establishes the grounding electrode vision for that application.

Terminology is very keen here and you need to understand that within your question. You are speaking of two different actions that seem to meld into once action. They are very different.

Hope this is helpful and if not please feel free to respond and we can discuss it in more detail as that is exactly what these forums are all about my friend.

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