UL508A Feeder Distribution

[JovialBulge]

In many of the “How to calculate SCCR” or “How to raise a panels SCCR” videos that I have watched recently on YouTube it seems as if one of the common sticking points for a panel having a low SCCR is the distribution block that’s usually located after the load side of the main disconnect in the feeder circuit.

If you only have say 2-3 branch circuits and each branch is protected by a set of fuses in a fuse holder, say Class CC for this hypothetical scenario. I don’t seem to see anything in the UL literature stating that you are unable to just wire from the load side of the main disconnect in the feeder, to the line side of the fuse block for branch circuit A and then loop from the line side of fuse block A to the line side of the fuse block for branch circuit B and then from B to C.

Panel cleanliness aside, is there something that I am missing where that would not be acceptable under UL508A?

 

[petersonra]

You can do this in some cases. Depends on how you do it.

For instance, if you have a 30 A main, you could run a 10 gauge wire from the main and use it to jumper the line side of how ever many branch circuits you have if the line side terminals are listed for two wires of 10 gauge.

Some small fuse blocks have accessory bus bars for this purpose.

I would want to see the particulars of what you have in mind before declaring it acceptable.

 

[JovialBulge]

It does seem as if the particular products that I have selected here will allow for single or dual wire on the terminal for the fuse blocks, so in theory I could do exactly as you stated and come from the disconnect load side with 10AWG and into the first fuse holders line side and then daisy chain as needed.

For my small application here, three branch circuits, I think this will be a simpler option versus a higher SCCR rated distribution block, or fused distribution block and other potential components that would need to be changed in the feeder. Although I may save some cost on going to a UL98 breaker as the main disconnect and having a fused distribution block after that, but I would rather not go further then required here.

 

[petersonra]

If you are using a mccb as your main, most times you can get what is called a distribution lug for the load side. It is usually a six hole lug instead of a one hole lug so can put six wires on it.

If you need more than six wires it is not unheard of for a small mccb with distribution lugs to be cheaper than a suitable distribution block.

There are also some distribution blocks listed for higher than typical sccrs when used with specified mccbs.

There are also distribution blocks rated above the normal range that do not require and special upstream protection. Marathon special products makes some that use studs for the connection. I think they are 30kA without any special upstream protection.