bonding bushing on Line/Load of transformer

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screamer

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Hello All, any help will be appreciated:

I have a 480/277V panel feeding a 150KVA x-fmr to a 208/120V panel. Is there any code article stating that I must use MIGB's (metal insulated grounding bushings)on the 30" of greenfield in or out of the x-frmr?
 
Re: bonding bushing on Line/Load of transformer

It depends the fitting and the wire size. The fitting may not require an insulating bushing by its design. Insulated bushings are required for conductors 4 AWG and larger see section 300.4(F)
I seldom use metal insulating bushings, for your application I would use a insulating bushing, as the transformer would vibrate and could damage the wires.
 
Re: bonding bushing on Line/Load of transformer

300.4 is only required where a raceway enters a enclosure. A fitting for FMC is not a raceway. The only raceway to me that would enter an enclosure would be of the threaded types. But as Tom stated the vibration would warrent an insulated bushing. As for requiring a grounding bushing? why FMC would not be allowed to be used as the EGC as it would only have a 60 amp rating and this transformer would have a fault current of over 400 amps. It would serve no purpose.
 
Re: bonding bushing on Line/Load of transformer

Originally posted by hurk27:
300.4 is only required where a raceway enters a enclosure. A fitting for FMC is not a raceway. The only raceway to me that would enter an enclosure would be of the threaded types.
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Wayne you and I differ on 300.4, IMO any raceway that connects to a enclosure with 4 AWG or larger requires a bushing.

EMT, FMC, LFMC, etc. all require bushings when used with conductors of 4 AWG or larger, or fittings with built in insulating matrial.

IMO you are reading to much into the word "entering".

I would fail inspection here in my area if I did not use bushings on EMT or FMC with 4 AWG or larger.

If you where writing that section of code what word would you use in place of 'entering'?

300.4(F) Insulated Fittings. Where raceways containing ungrounded conductors 4 AWG or larger enter a cabinet, box enclosure, or raceway, the conductors shall be protected by a substantial fitting providing a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by substantial insulating material that is securely fastened in place.

Exception: Where threaded hubs or bosses that are an integral part of a cabinet, box enclosure, or raceway provide a smoothly rounded or flared entry for conductors.

Conduit bushings constructed wholly of insulating material shall not be used to secure a fitting or raceway. The insulating fitting or insulating material shall have a temperature rating not less than the insulation temperature rating of the installed conductors.
Click to expand...
Bob

[ December 31, 2004, 05:50 AM: Message edited by: iwire ]
 
Re: bonding bushing on Line/Load of transformer

Gentlemen, let me clarify: I was referring to a grounding bushing. I intend to run an EGC in the FMC, but does it need to be bonded to the FMC on both or either end?

Thanks,

...Stephen Creamer
 
Re: bonding bushing on Line/Load of transformer

Stephen

In that case I can not give you a yes or no answer, all I can say is maybe.

You will have to look at 250.97 and decide if you need bonding bushings or not.

On the primary side you have over 250 volts to ground, that being the case you would have to use bonding bushings around a concentric knock out if it is not listed for that purpose.
 
Re: bonding bushing on Line/Load of transformer

screamer,I've been digging at this,and what I've finally come up with is:
250.118(6)
Listed flexible metal conduit,that is "NOT" listed for grounding,meeting -"ALL"- the following conditions.(must meet all),including "d" field-installing a EGC,still might not meet the needs.Parallel path for fault current might still exsist.See 250.96 also..I'm not sure this covers your question, 100% and is open for debate.And yes,I seen 250.97 also..
 
Re: bonding bushing on Line/Load of transformer

Bob you must have changed your view on this as you posted this when I had this question back in October :
iwire
Member
Member # 47

posted October 20, 2004 06:22 PM
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quote:
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When did the NEC start requiring an "Insulated" bushing to be installed on a SE cable fitting.?

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They haven't, the requirement is for raceways only.
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I agree it need's one because of the vibration from a transformer, but most fittings I have seen have a well rounded throat? As Dave (Websparky) has said it is a poorly written section.
 
Re: bonding bushing on Line/Load of transformer

Originally posted by hurk27:
Bob you must have changed your view on this as you posted this when I had this question back in October :
iwire
Member
Member # 47

posted October 20, 2004 06:22 PM
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quote:
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When did the NEC start requiring an "Insulated" bushing to be installed on a SE cable fitting.?

--------------------------------------------------------------------------------
They haven't, the requirement is for raceways only.
Click to expand...
I agree it need's one because of the vibration from a transformer, but most fittings I have seen have a well rounded throat? As Dave (Websparky) has said it is a poorly written section.
Click to expand...
No, same view. :)

That thread was about SE cable which is not a raceway.

My reply in this thread was regarding FMC which is a raceway.

Bob
 
Re: bonding bushing on Line/Load of transformer

Sorry I haven't posted lately been real busy.

I'm now seeing what your saying and it does make sense. Which would back the reason insulated bushings are needed in the first place.

What was confusing me was in the exception where is says;
Where threaded hubs or bosses that are an integral part of a cabinet, box enclosure, or raceway provide a smoothly rounded or flared entry for conductors.
Click to expand...
I can't think of a hub or a boss that would be a part of a raceway?
which was leading me to belive that it was meaning a fitting that was allowed to be the exception?
 
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