Working clearance for 13.8-480V power Transformers

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
Do the working access distances in Table 110.34 apply to transformers? Or is this only for switchboards, MCC’s, switchgear Panelboard, and disconnect switches?


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Yes.

It is not usually an issue because you typically have other required clearances as well.

Working spaces apply to equipment that are "likely to require examination, adjustment, servicing, or maintenance while energized".

Arguably, transformers get examined while energized. Kind of the only way to test them. Whether it is insulation tests, hot spot IR scans, etc.
 
Yes.

It is not usually an issue because you typically have other required clearances as well.

Working spaces apply to equipment that are "likely to require examination, adjustment, servicing, or maintenance while energized".

Arguably, transformers get examined while energized. Kind of the only way to test them. Whether it is insulation tests, hot spot IR scans, etc.

Years ago we had a similar scenario. The solution was to add double doors on the fence directly across from the transformer primary side along with a written procedure stating the doors had to open during examination or testing.
Not exactly a Code compliant
But the plant grudgingly accepted this resolution


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Years ago we had a similar scenario. The solution was to add double doors on the fence directly across from the transformer primary side along with a written procedure stating the doors had to open during examination or testing.
Not exactly a Code compliant
I have done this many times.
 
But this methodology is not listed as an exception correct?
Why would it be prohibited?

Are you thinking because the access doors/gates are barriers that have to be removed? I have not met an AHJ that uses this interpretation.
 
Why would it be prohibited?

Are you thinking because the access doors/gates are barriers that have to be removed? I have not met an AHJ that uses this interpretation.

The only true exception is “Working space shall not be required in back of equipment such as switchgear or control assemblies where there are no renewable or adjustable parts (such as fuses or switches) on the back and where all connections are accessible from locations other than the back…”
But I agree with you it should be allowed.


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As thorough as Code is, you’d expect some sort of an exception for ‘access doors’ to mitigate the required working clearances - otherwise it’s based on assumptions.


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What assumptions?
If the doors/gates aren't open you have no access. If you have no access you do not need clearance.

I know many electricians that will put their tools on the floor in front, along side of, or behind them while working on equipment to me this is more of a working clearance issues, than opening access doors/gates.
 
What assumptions?
If the doors/gates aren't open you have no access. If you have no access you do not need clearance.

I know many electricians that will put their tools on the floor in front, along side of, or behind them while working on equipment to me this is more of a working clearance issues, than opening access doors/gates.

There are many possible scenarios but I think the intent is to have the access doors closed while working on transformer and still be within the working clearances of Table 110.34.
Having said that, an operating plant would have ‘qualified individuals’ to service the transformer and in my opinion the access doors would be acceptable as long as there is written procedure just to ensure the procedure is followed


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There are many possible scenarios but I think the intent is to have the access doors closed while working on transformer and still be within the working clearances of Table 110.34.
Having said that, an operating plant would have ‘qualified individuals’ to service the transformer and in my opinion the access doors would be acceptable as long as there is written procedure just to ensure the procedure is followed


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What service would have to be done to an energized transformer??
 
What service would have to be done to an energized transformer??

Ideally none. But we know in the real world: hot oil reclamation, electrical testing, and various maintenance and repair procedures could happen


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Ideally none. But we know in the real world: hot oil reclamation, electrical testing, and various maintenance and repair procedures could happen


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Not energized
 
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