Tap of main buss
- Thread starter domnic
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If this is a tap of service entrance conductors then the feeder tap rules (10' & 25') do not apply. Have you done a load calculation?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Sure, but infinity's question is important. If it is "service panelboard" then it would be a 230.40 exception #2 installation to another grouped service disconnect - just make sure you wont be exceeding 6 disconnects total. If The conductors feeding the original panelboard are a feeder, then its a feeder tap. Either way the lugs would need to be listed for the combination and quantity of conductors you have.
sandsnow
Senior Member
- Location
- Southern California
Typically when lugs are rated for two wires, they have to be the same size, if memory serves.
there are a few items to take into consideration.
The "no main" causes some concern
Are you saying the existing 400 amp panel has no main ?
Is it a service panel ?
How many breakers are currently in the panel ?
What size conductors are feeding the existing panel ?
What is the total load calculation ?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Ok so the feeder tap rules dont apply. These are service entrance conductors so its a "service tap" which is really adding another set of service conductors. So my aforementioned code reference. Keep in mind you only have 380 amps of conductor (most likely) not 400. Also remember new panel is also a service panel so keep that in mind for your grounding and bonding. IF your lugs are not rated for the two different sized conductors, you could replace them with double hole lugs, or the panel may accept feed thru lugs.
- Location
- Massachusetts
I agree with all of this. (EDIT: It just occurred to me that we are assuming copper 500 kcmil with a rating of 380, it might be aluminum 500s with a rating of just 310 amps)
If you change the lugs on a panelboard I suggest ordering them from the panelboard manufacturer. If you use any old lugs off the shelf some inspectors might cite 110.3(B). I think that is over the top but I hate to redo work.
Last edited:
- Location
- Massachusetts
How did you come up with the 150 amps?
At this point in the thread we have determined you have multiple service disconnecting means and want to add another.
Code wise you now have some choices;
Size the service conductors for the total combined ampacity of all the service disconnecting means.
OR
Determine the true NEC exsiting load by doing load calculations or at least a month of current monitoring or get the demand load from the power company add the results of that to the new calculated load and make sure the result is less than the rating of the 500 kcmil service conductors.
You are not allowed to simply put an amp clamp on the existing service conductor read the current for a few seconds and call it 150 amps.
- Status