Understanding Space Requirements of Xfmrs and Disconnects

[ihope]

Hi,

I'm have some confusion regarding the space requirements of transformers and disconnect switches. What I understand from the code book is that transformers and disconnect switches need to be readily accessible and are subject to the conditions of NEC 110.26(A) Working Space, but not NEC 110.26(F) Dedicated Space (which only applies to panelboards, MCC, switchboards, etc.)

So, does this mean I can mount a disconnect switch over a transformer? I see a lot of installation like this and I'm not sure how the transformer is not intruding into the working space of the disconnect switch or impeding the accessibility of the disconnect. I guess technically for a small transformer, you would not need to climb over it to reach the switch.

Thanks!

 

[Smart $]

...

So, does this mean I can mount a disconnect switch over a transformer? ...

IMO that would be a violation of 110.26(C)(3), where part of the transformer extends beyond 6 in. from the front of the disconnect.

 

[ihope]

You're right - it would be a violation of 110.26(A)(3). Still, I'm very curious to know how so many installation of xfmrs under disconnect switches or panels passed inspection. I feel like I'm missing something.

 

[Smart $]

... Still, I'm very curious to know how so many installation of xfmrs under disconnect switches or panels passed inspection. I feel like I'm missing something.

Well, I don't know... but I always found it odd that this requirement is in a subsection titled "Height of Working Space" :?

 

[Gregg Harris]

IMO that would be a violation of 110.26(C)(3), where part of the transformer extends beyond 6 in. from the front of the disconnect.

What determinse the dimensions of the space? The transformer which would be required to be energized during examination, adjustment,servicing, or maintainence, or the disconect that is associated with it that is used to disconect power to the transformer.

 

[Smart $]

What determinse the dimensions of the space? The transformer which would be required to be energized during examination, adjustment,servicing, or maintainence, or the disconect that is associated with it that is used to disconect power to the transformer.

In general both, being that one has to extend more than 6 in. beyond the other to constitute a violation, but in this case, the disconnect determines nothing can be installed more than 6 in. frontward of it. It needs to be "adjusted" to connect and disconnect the transformer. Do not forget that clause is not just for when the energized part(s) are exposed. The general statement is considered foremost in the rationale.

110.26 Spaces About Electrical Equipment. Access and
working space shall be provided and maintained about all
electrical equipment to permit ready and safe operation and
maintenance of such equipment.