Additional Panel

[don_resqcapt19]

Re: Additional Panel

Bennie,
If we don't take an EGC to the second panel and use the grounded conductor for that purpose, we will have a silghtly higher voltage between noncurrent carrying parts that are bonded to the second panel and things like water pipes or building steel that are bonded at the building disconnect. This voltage will be equal to the voltage drop on the grounded conductor between the second panel and the first panel. If the EGC from the second panel would be connected to a common metallic system that also has a connection to the first panel, we have created a parallel path for grounded conductor current.
Don

 

[iwire]

Re: Additional Panel

Originally posted by don_resqcapt19:
Bennie is correct about this. The EGC is smaller than the grounded conductor and therefore would have a higher impedance. The higher the impedance of the fault clearing path, the longer the fault will exist.

Bennie has certainly made me think on that one there is no question about that.

If I have a long feeder from one building to another I would certainly consider using the neutral as the grounding conductor for that, if I could meet the requirements for doing so.

 

[engy]

Re: Additional Panel

Originally posted by don_resqcapt19:
engy,

Quote ”A cable assembly to a panel does not have to be 4 wires to be safer. It is actually more hazardous for the fact of slowing the fault clearing time.”

How do you figure that? NEC ground sizing requirements are inadequate?

Bennie is correct about this. The EGC is smaller than the grounded conductor and therefore would have a higher impedance. The higher the impedance of the fault clearing path, the longer the fault will exist.
Don

Yes Don, I understand all that. I thought Bennie was saying it was unsafe period. The EGC would still be properly sized.

 

[bennie]

Re: Additional Panel

Also: Grounding conductive material and equipment does not "limit the voltage to ground", it prevents a voltage to ground by dumping whatever energized the surfaces, and drains static charges.

 

[highkvoltage]

Re: Additional Panel

Ok here are the code sections.

100 Amp and less. Feeder coductor size use 60 deg C. 110.14(C)(1)(a)

Over a 100 Amp. feeder conductor size use 75 deg C. 110.14(C)(1)(b).

The deg rating is based on the equipment termial rating, basically the rating of the termination lugs ability to dissipate heat.

Feeders 215.2(A)(1) Since you are feeding a panel where the noncontinuous and continuous laods are unknown you would be subject to the greater value which would be 125% of either.

When you aply these sections to my calculations you will see that they were correctly figured.

 

[bennie]

Re: Additional Panel

Two subjects are being discussed. Next poster should start a new thread.

Panels can be loaded to 100% forever. Only the load is derated for continuous operation.

 

[iwire]

Re: Additional Panel

Originally posted by highkvoltage:
Ok here are the code sections.

100 Amp and less. Feeder coductor size use 60 deg C. 110.14(C)(1)(a)

Over a 100 Amp. feeder conductor size use 75 deg C. 110.14(C)(1)(b).

You are right with the code section but you left out an important part of it.

Part of 110.14(1)

Unless the equipment is listed and marked otherwise,

I doubt you will find any 100 amp panels that are not marked as 75 C, if you do I agree you would have to use the 60 C column.

Originally posted by highkvoltage:
Feeders 215.2(A)(1) Since you are feeding a panel where the noncontinuous and continuous laods are unknown you would be subject to the greater value which would be 125% of either.

If you do not know the load you can not decide what size panel to use either.

A 100 amp panel can not have a contiuos load in excess of 80 amps, it can have a contiuos load of 80 amps and an addtional non-contiuos load of 20 amps, so can the 3 AWG THWN.

If you want to run larger than required conductors go for it, I do quite often, but with 75 C terminals 3 AWG THWN is allowable for a standard 100 amp panel.

 

[iwire]

Re: Additional Panel

Originally posted by bennie:
Panels can be loaded to 100% forever. Only the load is derated for continuous operation.

2003 UL White Book

CIRCUIT BREAKERS, MOLDED-CASE AND
CIRCUIT BREAKER ENCLOSURES (DIVQ)

MAXIMUM LOAD
Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for 3 hours or more.

 

[bennie]

Re: Additional Panel

Six 20 amp circuit breakers loaded to 80% will equal 96 amps on the panel. This is in compliance.

Downsize the message, not the messenger.

[ March 04, 2004, 05:22 PM: Message edited by: bennie ]

 

[iwire]

Re: Additional Panel

How exactly do I derate a load and why would I want to?

Originally posted by bennie:
Six 20 amp circuit breakers loaded to 80% will equal 96 amps on the panel. This is in compliance.

I can not protect a 100 amp panel with greater than a 100 amp breaker, that breaker will not be in compliance.

 

[bennie]

Re: Additional Panel

Bob: You are one hell of an electrician. I stand corrected. My thinking is flawed.

[ March 04, 2004, 06:09 PM: Message edited by: bennie ]

 

[iwire]

Re: Additional Panel

Forgive me Bennie.

You challenge the establishment so your posts are some of the more interesting ones.

I guess you may be my Shane, if you know what I mean.

I will back off.

Bob

 

[bennie]

Re: Additional Panel

Bob: I'm just complaining, don't back off.

My oxygen ran out for a while.

I bet that's a new excuse for being wrong.

 

[drg]

Re: Additional Panel

A happy ending .....thats good for everyone.

Now if Bennie is willing he can explain things like where he used a western union splice and how long a #12 rat tail joint should be. These are not important things but things that are from Bennies past that he might know and care to share some info. in a different topic of course.

John

 

[highkvoltage]

Re: Additional Panel

Those code section refers to which column you use to select your feeders from Table 310.16. I never stated that a panel could not be 100% loaded. My references refer to conductor size and which deg reference you use. I was wrong when I posted 75 deg C for a 100 amp panel when it was 60 deg C. By the way I used Mike Holt's Electrical Formula NEC 2002 for the reference material. You would need 1/0 Copper or 3/0 Alum for these feeders. Neutral would be down sized and the equipment ground #8 Copper and #6 Alum 250.122.

 

[highkvoltage]

Re: Additional Panel

Bad typing. Neutral would not be downsized.

 

[bennie]

Re: Additional Panel

drg: No problem. I've made a few Western union splices. There is an inline and Tee tap splice.
An inline splice is merely twisting each wire around the other. One twist will be counter to the other. These joints are usually soldered with a gasoline blow torch. Sometimes paraffin wax is melted and wiped on the joint. This inhibits corrosion, and provides some insulation.

Do you mean Pig tail splice?

A pig tail splice is made by twisting the wires tight together, so they make a good electrical connection before being dipped in a solder pot.
These too can be wiped in paraffin to fill in and cover sharp ends. Rubber and friction tape was used for the finish. I always stripped about 2 inches and after twisting cut them to about one inch. I never spliced more wires together than could be easily cut at one time with sidecutters. This was about 5 No. #14's and 4 No. #12's.

 

[pierre]

Re: Additional Panel

Bennie
Now that the dead horse is lying or at least resting I am interested in some of the stories you used to start about your unusual work past. What was the living like down in the anartic? etc... How did you get picked for some of those jobs?

Pierre

 

[bennie]

Re: Additional Panel

Pierre: I would be glad to spin some of my sea stories, but they would not be related to the NEC.

The work was electrical but could not be referenced to the NEC.

 

[highkvoltage]

Re: Additional Panel

Bennie. You worked in the Artic? That is very cool.(Excuse the pun.) I would allow love to hear some stories. I have been looking at the construction projects down south and my wife and I have been considering it. I have also debated about putting an apt. to Alaska. I have a Journeyman Lineman Classification and a Journeyman Wiremen Classification. Any info you could share would be great.