Tap for a meter on 3 sets of 500MCM

[victor.cherkashi]

Attached is a sketch for clarification.

I am trying to determine a code-compliant method to tap a meter from a main feeder consisting of three sets of 500 kcmil conductors while complying with NEC tap rules.

Since the meter will be installed approximately 2 feet from the panel, NEC 240.21(B)(1), Taps Not Over 10 ft, applies. However, under this rule, the tap conductors are still required to have an ampacity of not less than 10 percent of the rating of the overcurrent device protecting the feeder 240.21(B)(1)(4).

This appears to require installing 100A-rated tap conductors feeding a small disconnect.

Is there any code-compliant alternative or exception that would allow a smaller tap conductor size in this scenario?

 

[infinity]

For field installed tap conductors that leave the enclosure the 10% rule applies. If the tap conductors do not leave the enclosure then the 10% rule doesn't apply. We typically see the OCPD integral to the enclosure to avoid the 10% rule.

 

[victor.cherkashi]

For field installed tap conductors that leave the enclosure the 10% rule applies. If the tap conductors do not leave the enclosure then the 10% rule doesn't apply. We typically see the OCPD integral to the enclosure to avoid the 10% rule.

In other words, are you saying that if you mount a new 30 A disconnect on the side of the panel, you can avoid the 10% rule? marked in red in the picture below.

 

[augie47]

Can you add a OCP device in the "BL" spaces ??

 

[curt swartz]

Can you add a OCP device in the "BL" spaces ??

I was wondering that too. Or since this just for voltage measurement equipment with minimal load tap into one of the feeders.

Is there an extra set of main lugs you were planning to use? If not how were you going to tap into all sets of the parallel conductors

 

[victor.cherkashi]

I was wondering that too. Or since this just for voltage measurement equipment with minimal load tap into one of the feeders.

Is there an extra set of main lugs you were planning to use? If not how were you going to tap into all sets of the parallel conductors

• Prefer to keep the black space available for future use.
• Tapping into three sets creates another complication. I believe each tap conductor would need to be #8 wire for each 500 kcmil to meet the required 10% (100 A) per phase. There no existing extra lug and no place to add one.

 

[synchro]

Can you add a OCP device in the "BL" spaces ??

• Prefer to keep the black space available for future use.

Could you use one blank space for a breaker feeding a subpanel to handle possible future loads?
And then in the other space a breaker feeding the meter to sense the voltage on the bus.

 

[infinity]

• Prefer to keep the black space available for future use.
• Tapping into three sets creates another complication. I believe each tap conductor would need to be #8 wire for each 500 kcmil to meet the required 10% (100 A) per phase. There no existing extra lug and no place to add one.

You cannot parallel #8 conductors. The minimum parallel size would be #1/0. Since this is a MLO panel I would find a place to tap the bus or add a lugs to the existing bolts.