Tap Rule Violation

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mull982

Senior Member
I came across another instance which I believe is a violation of the tap rule and wanted to hear others thoughts.

A 480V panel is being fed from an upstream 400A fused switch with a 600MCM cable. The 480V panel is a MLO and does not have a main breaker. Tapped directly off of the bus in this panel a #4AWG cable which goes on to feed another 480V MLO panel about 50ft away.

Looking at this I find this to be a violation of 240.21(B)(4) for a number of reasons:

1) Tap conductors are over 25ft long horizontally.
2) The 85A capacity of the #4 tap conductors is less than 1/3 (133A) the upstream 400A fused switch
3) The tap conductors terminate into a MLO panel and therefore do not terminate into a single OCPD.

Do you guys agree?
 
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petersonra

Senior Member
Location
Northern illinois
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engineer
mull982 said:
I came across another instance which I believe is a violation of the tap rule and wanted to hear others thoughts.

A 480V panel is being fed from an upstream 400A fused switch with a 600MCM cable. The 480V panel is a MLO and does not have a main breaker. Tapped directly off of the bus in this panel a #4AWG cable which goes on to feed another 480V MLO panel about 50ft away.

Looking at this I find this to be a violation of 240.21(B)(4) for a number of reasons:

1) Tap conductors are over 25ft long horizontally.
2) The 85A capacity of the #4 tap conductors is less than 1/3 (133A) the upstream 400A fused switch
3) The tap conductors terminate into a MLO panel and therefore do not terminate into a single OCPD.

Do you guys agree?
Click to expand...
I do. The fix is either to add a CB to the first panel or some kind of OCPD within 10 feet. My guess is neither fix is real palatable. OTOH, it has been there how long?
 
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mull982

Senior Member
petersonra said:
I do. The fix is either to add a CB to the first panel or some kind of OCPD within 10 feet. My guess is neither fix is real palatable. OTOH, it has been there how long?
Click to expand...

Thanks!

Why do you mention 10ft as opposed to 25ft? Is it because at 10ft the breaker can be a smaller size and only needs to meet the ampacity of the conductors and not 1/3 of the upstream supply?
 
infinity

infinity

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New Jersey
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Journeyman Electrician
A tap under the 10' tap rule would only need to be 1/10 of the ampacity of the OCPD ahead of the tap. So in this case your 400 amp OCPD would require a conductor with a minimum ampacity of 40 amps. Under the 10' tap rule the MLO is OK but if the panel falls under 408.36 it would require a main or other OCPD ahead of it.
 
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the blur

Senior Member
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cyberspace
I just seen a similar MLO subpanel, within 10 feet of the main service entrance panel, tapped off the main buss bars. So they are back feeding a 100amp breaker to feed the sub panel..... which is legal.

But here's my code question. It's NOT a bolt on breaker panel. just a 'press on' breaker. Doesn't the main in this situation need to be bolted in, or strapped down some how ? I remember coming across that somewhere in the book......
How can this be rectified ?
 
jumper

jumper

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the blur said:
I just seen a similar MLO subpanel, within 10 feet of the main service entrance panel, tapped off the main buss bars. So they are back feeding a 100amp breaker to feed the sub panel..... which is legal.

But here's my code question. It's NOT a bolt on breaker panel. just a 'press on' breaker. Doesn't the main in this situation need to be bolted in, or strapped down some how ? I remember coming across that somewhere in the book......
How can this be rectified ?
Click to expand...

408.36(D) Back-Fed Devices. Plug-in-type overcurrent protection
devices or plug-in type main lug assemblies that are
backfed and used to terminate field-installed ungrounded
supply conductors shall be secured in place by an additional
fastener that requires other than a pull to release the
device from the mounting means on the panel.
 
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the blur

Senior Member
Location
cyberspace
yes thank you, I knew I read that somewhere. So a few tie-wraps would make it legal ?? How else can you secure a press on breaker ?
Unless I can find a main breaker kit for a 20 year old GE panel board ?? which is unlikely.

Gotta love coming across someone elses mess.
 
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