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denman · Sep 1, 2013, 07:58 PM

Calling all electricians, here's what I've done. Installed main lug in detached garage. Ran 3 #3 wires and #6 ground. First went to 60 amp fusible cut off to protect panel components. Hots fit into lugs but neutral doesn't. So spliced them together with aluminum electrical splice. Drove 2 ground rods (6' apart) and tied into ground buss. Neutrals and grounds are separated and did not bond box. Now at the main panel hooked into 60 amp 2 pole breaker. However neutral does not fit in the neutral/ground buss. Does everything sound OK to this point and can I piggyback the neutral with the feed neutral under the mains neutral lug.thanks in advance for your help. D

Handyman2007 · Sep 1, 2013, 08:33 PM

You through the word "lug" around like crazy. I do not understand why the neutral wire will not fit the connectors in the box. That stymies me. I would have tio see that set up to make any more comments on this. Splicing the ground (earth) is a no no... Do you have less then 25 ohms between the earth rods? Too many questions

denman · Sep 1, 2013, 10:14 PM

Originally Posted by Handyman2007

You through the word "lug" around like crazy. I do not understand why the neutral wire will not fit the connectors in the box. That stymies me. I would have tio see that set up to make any more comments on this. Splicing the ground (earth) is a no no....Do you have less then 25 ohms between the earth rods?? Too many questions

Did not splice the ground. Spliced neutral wires together, which is essentially the same as tying the feed in to the connector in cut off box and then running the neutral out to the main lug panel from the other side of the same connector. No idea why holes are too small in diameter to accommodate the # 3 wire. From all the homework I've done ,I think I'm OK at the garage but couldn't get an answer if it was all right to piggyback the neutral (that goes to garage) under the same connector as the neutral feed to the main breaker panel goes under. Sorry, I'm trying to be as informative as I can , but sometimes my explanation is a little skewed. Thanks d

stanfortyman · Sep 2, 2013, 04:54 AM

Splicing the ground (earth) is a no no...

Sometimes yes. Sometimes no.

Do you have less then 25 ohms between the earth rods?

And just how is a diyer supposed to check this. Do you think he has the required $1000+ tester it takes? Do you? I don't.
Besides, he has two rods. The 25 ohm requirement goes out the window if you install two rods.

stanfortyman · Sep 2, 2013, 04:55 AM

however neutral does not fit in the neutral/ground buss.

You need to find out what brand panel you have and get a forked lug, or an add-on neutral lug for the bigger wire.
Most neutral/ground bars will take up to #4. After that you need an add-on lug.

Do not piggy-back two wires under one lug.

denman · Sep 2, 2013, 06:03 AM

Originally Posted by stanfortyman

You need to find out what brand panel you have and get a forked lug, or an add-on neutral lug for the bigger wire.
Most neutral/ground bars will take up to #4. After that you need an add-on lug.

Do not piggy-back two wires under one lug.

OK thanks

donf · Sep 2, 2013, 07:29 AM

Why are you using #3 AWG conductors and a #6 AWG neutral. A #3 AWG conductor can handle 85 amps and a #6 AWG conductor is 55 amps.

What is the distance from the main service panelboard to the downstream panelboard?

stanfortyman · Sep 2, 2013, 08:04 AM

Why are you using #3 AWG conductors and a #6 AWG neutral. A #3 AWG conductor can handle 85 amps and a #6 AWG conductor is 55 amps.

Don. #3cu THHN is good for 100A, not 85A.
#3NM cable is good for 85A which would typically be placed on a 90A breaker.

Also, he said a #6 ground, not neutral. A #6 ground is actually oversized for this feeder. A #8cu ground would have been fine.

donf · Sep 2, 2013, 09:58 AM

No where in the original post or subsequent posts is the type of wire discussed.

Nor is there any reason to believe that the panelboards or the fusible cut-off switch are listed for 90(C).

Which means to me that if the poster is using a listed 90(C) conductors, then the only reason to use them is for adjustment and correction purposes.

So, if they are listed 90(C) conductors they still can only be used as if they were in the 60(C) column which equals 85 amps.

Of course using the 80% load on the breaker this would allow up to 65 amps. Hey that answered my question! :)

Denman, what type conductors are you using?

stanfortyman · Sep 2, 2013, 11:05 AM

No where in the original post or subsequent posts is the type of wire discussed.

When was the last time you saw #3 NM cable?

Nor is there any reason to believe that the panelboards or the fusible cut-off switch are listed for 90(C).

Which means to me that if the poster is using a listed 90(C) conductors, then the only reason to use them is for adjustment and correction purposes.

So, if they are listed 90(C) conductors they still can only be used as if they were in the 60(C) column which equals 85 amps.

Who said anything about 90 deg C?
#3cu THHN in conduit with normal 75 deg C terminations is rated for 100A in the 75 deg C column or T310.15(B)(16) of the 2011 NEC.

Of course using the 80% load on the breaker this would allow up to 65 amps.

What rules is this? A breaker can be loaded to 100%.

donf · Sep 3, 2013, 04:58 AM

I must be having a brain dead moment Stan. Again, I come back to the fact that the poster has not indicated the listed connections of either the service panelboard or the disconnect switch in the garage.

without that information we can only use the 60(C) column. Also, if the conduit is to be installed underground, then THHN cannot be used because it is not listed for Wet areas.

Actually, I was using the 2014 (Pre-Release) edition of the NEC and I am not disputing the amperage of the wire. I am disputing the fact that without the proper listing information we cannot make the leap to the full value of the 90(C) listing.

stanfortyman · Sep 3, 2013, 04:46 PM

I must be having a brain dead moment Stan. Again, I come back to the fact that the poster has not indicated the listed connections of either the service panelboard or the disconnect switch in the garage.

Without that information we can only use the 60(C) column.

I haven't seen a 60 deg C termination in years. Most are 75 deg C with a few 90 deg as well. To assume terminations or breakers are 60 deg C is 1970's or 80's thinking.

Also, if the conduit is to be installed underground, then THHN cannot be used because it is not listed for Wet areas.

Probably for the 1,000,000th time... pretty much all new(er) THHN is dual rated THWN.
This correction does not have to be made any more.

denman · Sep 5, 2013, 05:31 AM

I'll have to get back to you on that. The work is at my nephews place. Can't get back there till Sun. You guys are talking way above my head, but I'm a fan of reading your posts back and forth.

donf · Sep 6, 2013, 03:55 AM

Denman,

On the inside of the metal boxes for both the panelboard and switch there should be information stamped into the metal. The name of the manufacturer, and within that data should be the "Listed" information. This will tell you whether the terminals of the switch and panelboard are listed for use up to 75(C) or limited to 60(C).

If both devices are listed at 75(C), then we can use the higher of the two amperages when selecting the cable. However if one is listed for 60(C) then we must select the cable from the 60(C) amperages.

I expect the panelboard to be listed at 75(C), it's the switch that is the unknown.