250.122(B) and How it can Bite You Hard.

[iwire]

I was just reading Ryan's post about raceways used as grounding means and I thought about 250.122(B), yes I know, I have to get a life.

Lets say you have post lights at the end of a long driveway.

The total load is 10 amps @ 120 volts, the length is 500' and you decide you want to keep the voltage drop to less than 5%.

This will mean you must run 6 AWG for the line conductors.

What size grounding conductor will be required, based on a 15 amp breaker?

Will you be able to use 6/2 UF cable out to the lights?

[ March 21, 2004, 10:47 AM: Message edited by: iwire ]

 

[pierre]

Re: 250.122(B) and How it can Bite You Hard.

Without doing the actual calculations (I am too lazy today), and based on experience, I would say that the 6/2 UF would be fine for this installation as far as the EGC is concerned.

Lets say that the installation for a 500 foot run indoors using EMT is installed without an EGC, using the conduit as the EGC. Would the conduit be sufficient as the EGC for such a length?

Pierre

 

[iwire]

Re: 250.122(B) and How it can Bite You Hard.

Originally posted by Pierre:
Without doing the actual calculations (I am too lazy today),

I doubt you are a lazy guy.

The beauty of 15, 20 & 30 amp circuits is that there are no calculations necessary.


PS, You might be digging up that 6/2 UF.

Bob

 

[bob]

Re: 250.122(B) and How it can Bite You Hard.

Iwire Posts
"The beauty of 15, 20 & 30 amp circuits is that there are no calculations necessary"

Why not?

 

[iwire]

Re: 250.122(B) and How it can Bite You Hard.

There are no calculations necessary as the ratio of the ungrounded conductors to the grounding conductors is one to one.

20 amp circuit

12 AWG ungrounded conductor and a 12 AWG grounding conductor.

Increase the ungrounded conductor size to 6 AWG and the Grounding conductor must be increased to 6 AWG.

In the example above the 6/2 UF will be a violation as the grounding conductor will be undersized.

 

[charlie b]

Re: 250.122(B) and How it can Bite You Hard.

Originally posted by iwire:12 AWG ungrounded conductor and a 12 AWG grounding conductor. Increase the ungrounded conductor size to 6 AWG and the Grounding conductor must be increased to 6 AWG.

I read the original post and went through the same thought process to say that a #6 EGC is needed. But help out a poor confused engineer: You say that a 6/2 UF would have an undersized EGC. But does a ?6/2 UF? even have an EGC?

 

[iwire]

Re: 250.122(B) and How it can Bite You Hard.

The trade can be as confusing as the code.

 

[bob]

Re: 250.122(B) and How it can Bite You Hard.

Iwire
Bob
I understand now what you were saying. The reason I asked the question was because the run was so long you would need to check the conductor size to ensure it was adequate. In this case the size of the #6 is adequate. In the other post I said that it was my understanding that table 250.122
was limited to about 100 ft. I had hoped that someone would verify this statement or to say they had never heard of this limit. The code gives no limit.

 

[roger]

Re: 250.122(B) and How it can Bite You Hard.

Here's a good UF chart.

Roger