What's in the box?

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Re: What's in the box?

Thanks Steve.
Have you ever been red tagged for not using an expansion joint on a PVC install? I ask because the two suppliers I use always look surprised whenever I ask for an expansion joint.
 
Re: What's in the box?

Have you ever been red tagged for not using an expansion joint on a PVC install? I ask because the two suppliers I use always look surprised whenever I ask for an expansion joint.
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No, I always use an expansion joint. There is a reason why the counter people at your supply house work there and not in the field. Its up to you to know when you need EJ not them.

Steve
 
Re: What's in the box?

Originally posted by coppertreeelectric:
4 cond. or not, you need a grounding electrode
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Just a quick lesson: SER has four wires, 2 hots, 1 ntrl and one GROUNDING ELECTRODE.

SER is used to feed a subpanel from the main. The main being the source of the grounding.

When you feed a main you use SEU that only has 3 conductors, 2 hots, one ntrl fed from the utility.

The moral of the story is: Use the grounding from the main by use of SER cable to feed a sub.

Steve
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I know what SER is and has and don't need a lesson on it, thank-you.
Do you ever read my posts???

I don't care if you decide to run a 4th wire for grounding, you will still need to drive a rod at the detached garage, period.
 
Re: What's in the box?

I know what SER is and has and don't need a lesson on it, thank-you.
Do you ever read my posts???
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I am sorry, I should have read further and did not realize it was detached. My apologies to you. I was in the wrong.

Steve
 
Re: What's in the box?

Re: another grounding electrode at the detached garage, the exception in 250.32 obviates the need for one if the building or structure is supplied by only 1 branch circuit and there is a grnding conductor.
I think I don't need one.
 
Re: What's in the box?

But I think I need to use 1 awg to allow for temp derating. These conductors will see ambient temps at 100◦F
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If you are using #2 THHN/THWN CU, you should be fine. At an ambient of 96 to 104 degrees F, the correction factor is 0.88 (see table 310.16, Correction Factors at the bottom):
#2 Cu THWN, 75 deg. col. = 115A X .88 = 101.2 Amp rating, derated for up to a 104 degree ambient.

At an ambient of 105 to 113 degrees, you would have to go to #1 to give you 100 amp capacity.

If enough of the conduit is in direct sun, you have to increase the ambient some more (above the air temperature), but I forget exactly how much.

If this was all in a dry location (overhead inside a building for instance), you could temp. derate using the 90 degree THHN rating from table 310.16.

[ April 04, 2005, 09:26 PM: Message edited by: tx2step ]
 
Re: What's in the box?

Panel and circuit breaker terminals are normally marked or "Labeled" or "rated" for 75 degree wire as well as for 60 degree wire. (i.e. they are usually marked 60 degree/75 degree) If everything you are connecting to is rated (marked) 75 degrees, then you can use the 75 degree column.

Since this is a feeder from a circuit breaker to the main lugs of a sub-panel, the terminals at each end should be rated for 75 degree wire. (check and make sure, though)

If everything you are connecting to (i.e. the terminals at each end) is rated (marked) for 90 degrees, then you could use the 90 degree column for the base rating of that run of wire.

If the terminals at one end of the wire are rated 75 degree but the terminals at the other end are only rated 60 degree, then you must use the lower 60 degree rating.

Most wiring devices (plugs, switches, etc.) are only rated 60 degrees, so for branch plug and lighting circuits you are normally limited to the 60 degree column.

Normally, it is the temperature rating of the terminals that dictate the maximum temperature rating allowed for the wire that is connected to it. See 2002 NEC 110.14 (C)

Terminals of equipment rated over 100 amps or rated for conductors larger than #1 AWG are almost always rated at least 75 degrees (See 110.14(C)(1)(b). (but I'm sure there are exceptions, so always look)

For derating the ampacity of the wire for ambient temperatures that it is exposed to: If the temperature rating of the wire is higher than the temperature rating of the terminals, you can use that higher ampacity rating of the wire (i.e. at that higher temp rating) to derate from for ambient temperature correction of the wire only (to temperature derate the wire only), as long as you don't derate the wire to below the amperage listed for the temperature rating of the terminals.

If you have a NEC handbook, then there are examples and further explanation there on how to do it.

If you don't have a NEC handbook, then I recommend that you get one -- they're very helpful. They are now available for the 2005 NEC. I think that mine cost about $120.

[ April 04, 2005, 09:52 PM: Message edited by: tx2step ]
 
Re: What's in the box?

Thanks Tx,
Yes I have the 2002 NEC + Handbook.
I do understand the ratings of the terminals as the limiting factor of safe operation. The technology of plastics has provided very high operational temps for the wires, but the terminations are the weak link. But to simply look at the damn things and read what they are rated...all I can say is DUH. I have a 200 amp Siemens main breaker right on my desk and guess what...it says 75◦C. Right on TX.
 
Re: What's in the box?

Originally posted by jjhoward:
Re: another grounding electrode at the detached garage, the exception in 250.32 obviates the need for one if the building or structure is supplied by only 1 branch circuit and there is a grnding conductor.
I think I don't need one.
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What?? :confused:

You have a feeder to the detached garage, not a branch circut, so, you need the electrode as per 250.32(A). The Exception does not apply to your design.
 
Re: What's in the box?

If there exist no grounding path back to the main structure and the conduit run is PVC the ground conductor is not neccesary and would be preferred to have a ground electrode at the sub location, correct, like how I tell you guys how to do it then ask for approval.
 
Re: What's in the box?

Hi Luke,
I am confused about the term "feeder". Is the cable from a main breaker panel to a sub a feeder or a branch circuit?
If it is a feeder, then the size of the conductors can be taken from table 310.15(B)(6). If this is acutally a branch circuit, then I must refer to table 310.16 for wire size. So which is this? Checking the definition of Feeder, I agree with you this is a feeder. So... I can use 4 awg copper for my 100 amp sub panel?
 
Re: What's in the box?

If this 100 amp circuit was feeding a welder or a compressor, it would be a "branch circuit, individual" because it would be the last overcurrent device supplying one utilization equipment.

Since it is feeding a panel in a detached garage, it is a "feeder". The circuit breakers in that panel will feed the branch circuits in the garage. Even if you only install one branch circuit initially, it is still a feeder because more branch circuits can be added to the panel, and the last overcurrent device still is in that panel.

Look in you 2002 NEC Handbook, page 25, exhibit 100.5 for a clear distinction between feeders and branch circuits. Also read the definitions for branch circuit and for feeder.

310.15(B)(6) specifically says it only applies to a feeder to a dwelling ("...feeder conductors that serve as the main power feeder to a dwelling unit...") A detached garage isn't a dwelling unless it specifically meets that definition (the definition at the front of the code book, Article 100). This would probably be a judgement call for the AHJ, but most of them that I know wouldn't let you use table 310.15(B)(6) for a feeder to a detached garage.

How did you come up with needing a 100A feeder and panel for the garage? Do the loads there require that size panel? If you are wanting to use #4,can you get by with using a circuit breaker rated at or below its adjusted amp rating?

Was this a bid job?

If you are doing it by the hour, I'd just feed it with #2, a 100/2 CB in the main panel, and use a 100A MCB panel in the garage, and get on with it. A MCB panel will probably be cheaper, and you can kill the whole panel locally if you need to work on it or if something serious happens in the garage.

[ April 05, 2005, 07:50 PM: Message edited by: tx2step ]
 
Re: What's in the box?

Joe, it's a feeder.

I pretty much agree with tex on his above post.

The debate now is which table do you use.

As tex stated above, alot of inspectors or AHJ's won't allow you to use Table 310.15(B)(6) for this application, some will.

Article 310.15(B)(6) goes on to state that "...For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circut panelboard(s)."

It has been debated before on this forum, that sentence allows you to use Table 310.15(B)(6). Which would allow you to use #2 AL or #4 CU to feed your 100amp panel.
Then there is the other side of the debate which says you can't.
 
Re: What's in the box?

Thank you for the input Luke and Tx.
This job is for a h.o. who is purchasing this pretty pricy home (~$1meg or more) that has an attached 2 car garage and a detachted 3 car garage. This guy is a "hobbyist". He builds kit cars. This is body work, light duty welding (120v Mig welder), painting(240V 30amp compressor). He REALLY wants a 100 amp sub panel in this garage which will be his new playground. So I think it is better to run the 2 awg CU to be certain his lights don't dim in the house while he is playing. I think one of his cars will be featured in Kit Car magizine in August.
 
Re: What's in the box?

Originally posted by coppertreeelectric:
a conductor used to establish electrical contact. :D

Unfortunately for you, the NEC provides a definition of "grounding electrode" that overrides the english definition. "A device that establishes an electrical connection to the earth."

Keep your terms straight. :D :cool:
rolley.gif
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Re: What's in the box?

"grounding electrode" "A device that establishes an electrical connection to the earth."
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George, Your post said
SER doesn't contain electrodes. It contains conductors
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You are in fact wrong. There is a difference between the definition of ELECTRODE and GROUNDING ELECTRODE. A grounding electrode is a path to earth. But any type of conductor is an electrode as the definition by either the English or electrical dictionary and common sense a electrode is a conductor used to establish electrical contact.

But lets not get too spicific. I was only joking.
 
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