Flex connections required to transformers?

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kerajam

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Has anyone had any trouble from inspectors for hard piping to transformers instead of flex? With the windings of newer transformers on internal dampening pads it seems like a doable idea since the case would be isolated from vibration. This would save the hassle of having to deal with equipment ground transitions in longer conduit feeds to the transformer. Thanks.
 
kerajam said:
Has anyone had any trouble from inspectors for hard piping to transformers instead of flex? With the windings of newer transformers on internal dampening pads it seems like a doable idea since the case would be isolated from vibration. This would save the hassle of having to deal with equipment ground transitions in longer conduit feeds to the transformer. Thanks.
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granted my experience is limited (2 years), but NO job I've been on thus far has had hard pipe going directly to the xfrmr.
 
Transformers

Transformers

I have the same question about pipe versus flex to transformer. I recently ran 2" rigid on the primary side from the MCP to a 30KVA transformer and flex from on the secondary side. There is no noticeable vibration (I installed rubber grommets on the feet) and the noise is almost non-existent. A non-electrical Project Manager has questioned my use of rigid saying it is not to code. I can not find a reference to this in article 450. Does anyone have an answer? On the same job - at the main switch gear - I ran two parallel runs of 4" EMT to a 125KVA Transformer pipes all the way. That was inspected by 3 separate Electrical Engineers - if that is okay and the smaller one is not -why?
 
I agree with barbeer,

There is no NEC requirement that prohibits the use of a solid raceway for connecting transformers. It is a good trade pratice to install a flexible connection but not required.

Sometimes people get into the habit of thinking things that are good trade pratice are actually code when they are not.

Chris
 
clarice said:
A non-electrical Project Manager has questioned my use of rigid saying it is not to code.

. . . if that is okay and the smaller one is not -why?
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These are questions you should ask the people claiming they are not compliant - the moment they say it - including the NEC section.
 
raider1 said:
Sometimes people get into the habit of thinking things that are good trade pratice are actually code when they are not.

Chris
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Well put, I agree with that statement 100%. I am always correcting people at work on what's "ACTUALLY" code and what's a trade practice.
 
larger transformers have been installed using wireway, which would be the same as not using flex...and you would think that larger transformer would vibrate more.
P.S.
There is no NEC code violation for not using flex.

There may be a manufacturer that has the wiring method spelled out in the instructions, but I have not seen it.
 
If you've ever had to change out a failed transformer, you'll appreciate the flex connection. No code on it, but a fine installation technique in any event.
 
When installing large conductors to a relatively small area in the lower portion of the large transformer, you will not be thinking of taking it apart in the future, and you will certainly be relieved with the relative ease in entering the transformer with the wireway, as opposed to the conduit/flex, especially when the areas around transformers are usually cramped to start with. Bend baby bend.
 
I think most people use flex so they can use the 90 degree connectors to bring the feeders to the front of the transformer and below the heat line determined by the manufacturer.
I have mounted pull boxes to the side of a transformer, and piped out of the pull box.
 
There was a long disscusion here once about using a flexible metal conduit to protect a gec run into a transformer. As I remember 250.64 (B) prevents that, so its either single conductor ac cable or a hard pipe for that.
 
Pierre C Belarge said:
When installing large conductors to a relatively small area in the lower portion of the large transformer, you will not be thinking of taking it apart in the future, and you will certainly be relieved with the relative ease in entering the transformer with the wireway, as opposed to the conduit/flex, especially when the areas around transformers are usually cramped to start with. Bend baby bend.
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Recently I've started to see transformers that allow conduit entries near the top of the transformer. I believe they're made by Rex Manufacturing.
 
I was surprised too. The transformer actually had the secondary connections on the top above the core. I believe it was a 225 KVA. I see if I can get a photo next week.
 
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