another electrical question.

[tbird175]

I want to feed a subpanel from a 200 amp service panel from a tap on the load side of the disconnect breaker. the sub panel is a 100 amp main lug type. The panels are less than 1 foot apart. I want to feed the sub panel through a 80 amp breaker in the sub panel. Will the 80 amp breaker protect the sub panel with the power flowing through it backwards? I am not concerned about the any physical damage to the wire from the 200 amp panel to the sub panel, it is in a 1' run of conduit.

 

[211libwtfo]

So you going to land your sub panel feeders on the load side of an 80a breaker to back feed the panel for branch circuits......that will work, nice job!!! My one question is did you put a ground rod in at the garage? Or did you carry over a four wire system?uffer ground?

 

[bigdee]

Not directional UNLESS marked 'line' and 'load'. If not marked it is legal. You have to label it as "main".

 

[tbird175]

I thank all of you again for your information. I am locating a ground rod at the shop to keep the shop ground separate from the house. The 80 amp breaker is not marked line and load and I will label it main.

 

[bigdee]

So you going to land your sub panel feeders on the load side of an 80a breaker to back feed the panel for branch circuits......that will work, nice job!!! My one question is did you put a ground rod in at the garage? Or did you carry over a four wire system?uffer ground?

Read NEC 250.32 it was changed in 2008. 4 wire service AND grounding rod required. Neutral must float and cannot be used for grounding. Neutral has to be isolated from the 4th conductor (equipment ground). This is to prevent parallel current paths on the neutral conductor. This only applies to feeder circuits to a distribution panel....it does not apply to branch circuits.

 

[tbird175]

My plan is to pick up a new isolated ground at the shop and not bond the neutral and ground in the sub panel in the shop. Will this be okay?

 

[211libwtfo]

Here to feed a sub panel you must bring a 4 wire and use a uffer ground and naturally the neutral isn’t bonded.

 

[bigdee]

Here to feed a sub panel you must bring a 4 wire and use a uffer ground and naturally the neutral isn’t bonded.

That is correct. The 4th wire is the equipment ground and will connect to shop panel ground bus along with earth ground rod. Neutral will connect to a separate bus bar electrically isolated from equipment grounds. In other words you cannot use the neutral for a ground....even though it is grounded at origin.

 

[tbird175]

I understand that the NEC says you must run a separated ground wire to a sub panel. I hate to keep pestering you all but what is the difference in grounding back through the fourth wire to the power company pole versus having a separate equipment ground at the shop panel isolated from the service ground? I have no problem in the shop area obtaining a good ground.

 

[bigdee]

I understand that the NEC says you must run a separated ground wire to a sub panel. I hate to keep pestering you all but what is the difference in grounding back through the fourth wire to the power company pole versus having a separate equipment ground at the shop panel isolated from the service ground? I have no problem in the shop area obtaining a good ground.

NO you misunderstood. Shop HAS TO BE GROUNDED through 4th wire TO service entry panel. You still have to have a ground rod at shop and it will also be connected to this 4th wire (equipment grounding conductor). It is the neutral conductor that is to isolated (separated) from the ground at shop. It will be grounded at service entry only. Look up NEC 250.32b on google it might explain better than I. Everything down stream of your service entry (meter) has to be bonded back to the meter....no exceptions. In old days they used the neutral for grounding since it is grounded at its origin. Even though neutral has zero voltage and is grounded at meter it is one of the current carrying conductors and can only be used as such.

 

[tbird175]

OK I stand corrected. The older codes which I more familiar with (showing my age) did allow this when there,was no other connections between the two panels such as metal conduit, metal water lines, metal gas lines, etc.