Service Entrance and other matters

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Old 06-06-04, 03:11 AM
doingitmyself
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Service Entrance and other matters

I've placed this as a new thread, and I apologize if this is worrisome, but I thought some more ppl might want to add thoughts. Not to discount all of winnies help, but it would be nice to hear from others too

Re; GE panel: OK, we're making some progress, but..........

the SE cable from the house is 6/4wg (60 amps). Went to Lowes, couldn't find a 60 amp breaker panel - only thing they had in 60 amps were main lug only. I wanted a damn breaker to disconenect the power, but the best they could do me was a 100 amp main breaker. Man at Lowes told me that my branch circuit breakers (provided they were 60 amp or less) would provide protection to the 60 amp SE cables, and that it would be OK to use the 100 amp breaker. At first, I didn't believe this, but, of course now, I'm second guessing myself again. But isn't this a truth, in fact? Would not the branch CB, in fact, shut off before the #6 SE wires became damaged from an overload or overcurrent condition?

Seeing that the SE feeder was only 60 ampacity, I decided to buy an EGC grounding kit, a ground rod and #4 bare copper wire. I plan on separating the grounds and neutrals tomorrow, installing the ground rod and the #4 bare ground.

Questions follow:

As the current situation is, there is, in fact, no protection at all for the SE cables since there's no main breaker, so,

1). Would not the branch CBs, in fact, shut off before the #6 SE wires (un)protected by a 100 amp main became damaged from a fault, overload or overcurrent condition? This is assuming we would buy the 100 amp breaker panel.

Unknown to me before today, my friend has an arc welder (an antique, I think - specs to follow) in the garage that he also wishes to use as well as the air compressor and some hand tools such as drills, etc. I did not know this before today, so,

2). What is the normal/usual ampacity of arc welders? And, will this 60 amp service that he currently has be sufficient?

The specs (from the metal plate)of his welder are as follows: the primary shows an ampacity of 37 amps @ 230 V. The secondary shows amps of 180!!! What's the difference here?

3). Surely we don't need a breaker to cover 180 amps?

I used a clamp on ammeter on the branch circuit wires to the welder receptacle, and there was 2.9A when the welder was not in use (only turned on), but when the welder was in use, the current ran up to 47a - this is protected by a 60 amp branch breaker.

Thanks,
-Terry
 
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Old 06-06-04, 04:55 AM
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I didn't see the other post, but be sure your subpanel is fed with three insulated conductor plus the ground SE Cable.
The 60A CB in the main panel would protect all equipment downstream at 60A. You can place a 100A panel downstream, and it would be protected at 60A.
 
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Old 06-06-04, 05:45 AM
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Get the 100A subpanel, it will be fine.

The 100A main breaker in the subpanel will _not_ provide protection for the conductors. But this is okay, since the 60A breaker in the main panel that feeds this panel will provide the necessary protection. The 100A main breaker will simply be used as the disconnect for the detached garage where this panel is located.

In general the branch circuit breakers cannot be depended upon to protect the feeder conductors. There are situations in which they will provide the needed protection, but you don't want to depend upon this here; you want the flexibility of having branch circuit breakers which total more than the feeder capacity, since only some of the tools will be used at one time.

Welders are a different, and complex story. There is an entire section of the NEC dedicated to welders, with different rules that are sometime counterintuitive if you know standard wiring rules. Each welder has a different set of requirements; there are not 'typical' values. We need some additional information on the welder name-plate to answer your questions. You have already told us the 'primary' rating of 37A. We also need to know the 'duty cycle' rating, and also any instructions from the name plate regarding branch circuit protection (circuit breakers or fuses) and conductor ampacity (AWG, gauge, or amps). Check the nameplate and report these values or report that the nameplate doesn't mention these items (they will not all be there).

With the information provided, I can say that the 60A feed is sufficient to run this welder. It is also quite likely that the branch circuit which you mentioned (10ga wire on a 60A breaker) is actually appropriate for this welder, even though normally 10ga wire must be protected at 30A.

-Jon
 
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