Absurdly Simple Question II: Transformers

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George Stolz

George Stolz

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Where would I find a requirement for locating a disconnect on the line or load side of a typical 480 - 120/208Y transformer supplied by a 150A primary breaker?
 
an absurdly simple question from you scares me more than a snake:grin:
both may bite you....
Would 240.21(C) not cover the need and location for a secondary disconnect.
Under '08 and earlier, there is no requirement for a primary disconnect.

come on snake...
 
How about this for 2011-- all new


450.14 Disconnecting Means. Transformers, other than Class 2 or Class 3 transformers, shall have a disconnecting means located either in sight of the transformer or in a remote location. Where located in a remote location, the disconnecting means shall be lockable, and the location
shall be field marked on the transformer.
Click to expand...
 
augie47 said:
an absurdly simple question from you scares me more than a snake:grin:
both may bite you....
Click to expand...

LOL

A guy from work hit me up today, said one guy passed on the answer for the moment and another came up with something off the cuff. When I went looking (in the 2008 since it was a 2008 installation) I was a little surprised to see a void where disconnecting requirements would normally be.

I had never really thought about it, and have heard a lot of wives tales about this. Usually, I'm too busy with the task at hand to think about second-guessing what I've been told to do.

augie47 said:
Would 240.21(C) not cover the need and location for a secondary disconnect.
Click to expand...

Overcurrent protection, but not disconnection. They are almost always dealt with separately in the code.

augie47 said:
Under '08 and earlier, there is no requirement for a primary disconnect.
Click to expand...

iwire said:
There has never been one as far as I know up until the 2011 NEC and that is at the office.
Click to expand...

Does that strike anybody else as odd? All these years, no requirement to have a disconnect on a transformer?

Dennis Alwon said:
How about this for 2011-- all new
Click to expand...

Thanks, Dennis. :)
 
George.,.,
Yes..240 is OCP, but I did not think about it until it was too late. In practice the OCPs I see are usually a disconnecting device also... NEC (and you) keep us on our toes

Bob,
I agree. I haven't read the ROPs, but one does wonder why it was added after all these years. Disconnect sales must have slipped. :grin:
 
It was added in the opinion of increasing the level of safety for qualified electrical workers who may need to work on or perform maintenance on the XFMR. Sounds like a smart move to me. This change simply brings XFMRs in line with similar requirements for motors, generators, appliance and so on.
 
radiopet said:
It was added in the opinion of increasing the level of safety for qualified electrical workers who may need to work on or perform maintenance on the XFMR. Sounds like a smart move to me. This change simply brings XFMRs in line with similar requirements for motors, generators, appliance and so on.
Click to expand...

So in other words, 'Just because' without and real issue being used to substantiate the need.:roll:
 
iwire said:
So in other words, 'Just because' without and real issue being used to substantiate the need.:roll:
Click to expand...

No more than for any other piece of equipment.
If one is not needed for a transformer then why would one be needed for any other piece of equipment?
Some where some how common sense comes into play.
 
9-176 Log #3821 NEC-P09 Final Action: Accept in Principle
(450.14)
_______________________________________________________________
Submitter: James J. Rogers, Bay State Inspectional Agency
Recommendation: Add new text to read as follows:
450.14 Disconnecting Means. Transformers other than listed class 2 or class
3 transformers shall have a disconnecting means located either in sight of the
transformer or remotely provided the remote disconnect is capable of being
locked in the off position. When the disconnecting means is located remote
from the transformer the locking means required shall remain in place whether
or not the locking means is installed.
Substantiation: Requiring a disconnecting means for a transformer is intended
to enhance safety for the qualified individual that is required to work on the
transformer. This is especially true in installations utilizing the requirements of
240.21(B)(3) whereby there may be several transformers in different locations
all tapped from one feeder and it may be impractical to de-energize the entire
feeder system to work on one of the transformers.
Panel Meeting Action: Accept in Principle
Revise the rule to read as follows: ?Transformers, other than Class 2 or Class
3, shall have a disconnecting means located either in sight of the transformer or
in a remote location. Where located in a remote location, the disconnecting
means shall be lockable, and the location shall be field marked on the
transformer.?
Panel Statement: CMP-9 has made editorial changes to avoid a run-on
sentence, used ?open? instead of ?off? for the disconnect position in
accordance with customary code usage, used ?where? instead of ?when?
because it is a question of place and not time, and removed the listing
limitation on the Class 2 and 3 transformers because it has no bearing on
whether a disconnecting means needs to be installed. The lockable wording
correlates with the task group results reported in Proposal 9-201.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
Comment on Affirmative:
YOUNG, R.: The disconnecting means should be lockable in the open
position whether or not the disconnecting means is mounted either within sight
of the transformer or in a remote location.
 
jwelectric said:
No more than for any other piece of equipment.
If one is not needed for a transformer then why would one be needed for any other piece of equipment?
Click to expand...

Like motors? Which often require service and have moving parts.

Like appliances? Which often require service.

OTH transformers do not often require service and the people who would be serviceing transferomers would presumable be well quilifed and know they are required to do LOTO back at the source.


Some where some how common sense comes into play.
Click to expand...

Exactly and this new code section lacks all traces of it.

It is not commonsense to make a rule just for the sake of making things 'the same' the equipment and needs of the equipment are very different.
 
Substantiation: Requiring a disconnecting means for a transformer is intended
to enhance safety for the qualified individual that is required to work on the
transformer. This is especially true in installations utilizing the requirements of
240.21(B)(3) whereby there may be several transformers in different locations
all tapped from one feeder and it may be impractical to de-energize the entire
feeder system to work on one of the transformers.
Click to expand...

There is no evidence contained in that substantiation that this has actually been a problem.

As far as things being 'tapped from one feeder and it may be impractical to de-energize' that clearly sounds like a design issue.

That same argument could be used to justify everything from mains in every panel to reducing the amount of circuits allowed in each panel.
 
iwire said:
Like motors? Which often require service and have moving parts.

Like appliances? Which often require service.

OTH transformers do not often require service and the people who would be serviceing transferomers would presumable be well quilifed and know they are required to do LOTO back at the source.




Exactly and this new code section lacks all traces of it.

It is not commonsense to make a rule just for the sake of making things 'the same' the equipment and needs of the equipment are very different.
Click to expand...

iwire said:
There is no evidence contained in that substantiation that this has actually been a problem.

As far as things being 'tapped from one feeder and it may be impractical to de-energize' that clearly sounds like a design issue.

That same argument could be used to justify everything from mains in every panel to reducing the amount of circuits allowed in each panel.
Click to expand...

Well said Bob and I agree.

IMHO a panelboard is more likely to require examination or service than the typical dry type transformer, but a panelboard does not require a local disconnect. The substantiation for this requirement is quite lacking.

Motors and appliances require routine maintenance whereas a dry type tranformer does not require the same level of maintenance.

Chris
 
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Personally, I am indifferent to this new requirement. I just install whatever I am told to. Here is what MH says about it.

450.14 Disconnecting Means. For transformers other than Class 2 and Class 3, a means is required to disconnect all transformer ungrounded primary conductors. The disconnecting means must be located within sight of the transformer unless the location of the disconnect is field-marked on the transformer and the disconnect is lockable. (click here to see Fig. 17)

Analysis: Although many Code users have believed that this requirement already existed, in previous NEC editions transformers were one of the only pieces of equipment that didn?t require a disconnecting means. Although there were no documented injuries to warrant this change, it?s hard to argue that this requirement doesn?t enhance safety.
Click to expand...

http://ecmweb.com/nec/2011-nec-changes-20101101/
 
I also agree with Bob.
It?s reasonable to require ?safe? over ?unsafe? and basically ignore the costs; but requiring ?safer? over ?safe? should also include a sound economic justification.
 
I did notice that the language in the proposal for the locking means to remain in place did not make it into the 450.14. Does this mean typical LOTO devices could be used as long as the circuit number or disconnect location is marked on the transformer?
 
iwire said:
It is not commonsense to make a rule just for the sake of making things 'the same' the equipment and needs of the equipment are very different.
Click to expand...

jwelectric said:
Now this of course in nothing more than your opinion, is it not?
Click to expand...

No.

It is a fact that motors and transformers are different

It is a fact the servicing needs are different

It is a fact the potential for personal injury is different

It is a fact that the only reason offered for this code change was an opinion and not evidence of a problem with the previous code cycles
 
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