More main panel/subpanel questions.

[gayler]

Years ago when we bought our house, it's a mobil home the disconnect on the pole outside was a breaker box with two 40a screw in fuses. I took the advice from the city electrical dept and bougjt a Square D homeline exterior box and a 100a breaker for it and he put it in for me. When the garage was built he came back and ran the wires from my mast to the pole, not running to my Square D box on the pole. A few years down the road I decided I would like a disconnect so I bought another breaker and he wired it up for me. Correct me if I'm wrong but wouldn't my box in the garage be a sub box needing a ground wire run from the disconnect on the pole?

 

[ishiboo]

Yes and no.

I believe in the 2008 NEC update this changed. It would now be required, was it when you did it? Perhaps not.

IMO this is a marginal improvement if any and there's no reason for concern, as long as the box in your house and garage are both wired properly - with the ground bus bonded to the neutral.

Having disconnects on the pole is great IMO as you can then disconnect both your panels completely for maintenance, replacement, etc.

 

[wyliesdiesels]

First off, yes, if there's a disconnect on the pole, then u need a 4-wire feed to the garage. The other thing is, u said the 40a fuses were upgraded to a 100a breaker. Did u upsize the wire? I sure hope u didn't protect a #8/40a wire with a 100a breaker!....

 

[wyliesdiesels]

Yes and no.

I believe in the 2008 NEC update this changed. It would now be required, was it when you did it? Perhaps not.

IMO this is a marginal improvement if any and there's no reason for concern, as long as the box in your house and garage are both wired properly - with the ground bus bonded to the neutral.

Having disconnects on the pole is great IMO as you can then disconnect both your panels completely for maintenance, replacement, etc.

Incorrect! Ground and neutral should be bonded only in the first/service/main panel. All panels after that, should have an isolated neutral!

 

[Falcon67]

ishiboo has the data on this. My old shop was fed the same way. Meter-> disconnect -> 3 wire garage feed ->panel w/ ground. Lots of farm outbuildings wired like that. I have an old code book from 199x that clearly shows this method as kosher. Now, 4 wires is the norm.

 

[gayler]

First off, yes, if there's a disconnect on the pole, then u need a 4-wire feed to the garage. The other thing is, u said the 40a fuses were upgraded to a 100a breaker. Did u upsize the wire? I sure hope u didn't protect a #8/40a wire with a 100a breaker!....

The wire for the garage is properly sized. Not sure of the size on the house but I think it is.

 

[pattenp]

ishiboo has the data on this. My old shop was fed the same way. Meter-> disconnect -> 3 wire garage feed ->panel w/ ground. Lots of farm outbuildings wired like that. I have an old code book from 199x that clearly shows this method as kosher. Now, 4 wires is the norm.

It's a matter of when the install was done. Old NEC vs. New NEC.

 

[gayler]

I swear my whole town is wired by a bunch of hacks. I'm a hack too, but I'm trying to learn and do things right.

 

[gayler]

It's a matter of when the install was done. Old NEC vs. New NEC.

I know the garage was built in 2002. Is it a safety concern to be wired three wire as opposed to four?

 

[wyliesdiesels]

I know the garage was built in 2002. Is it a safety concern to be wired three wire as opposed to four?

The reason code was changed was because of safety. The issue arises when there are parallel electrical paths between buildings(water line, gas line, etc.) and the intended return path(neutral wire) becomes disconnected, corroded/highly resistant, etc., and then current starts straying and returning on one of the unintended/undesired ground electrical paths between the buildings!

It's a matter of when the install was done. Old NEC vs. new NEC.

I keep forgetting that 4-wire feeds weren't always the norm or code... : / But regardless of code, 4-wire feeds are always safer than their 3-wire counterparts!

 

[ishiboo]

The reason code was changed was because of safety. The issue arises when there are parallel electrical paths between buildings(water line, gas line, etc.) and the intended return path(neutral wire) becomes disconnected, corroded/highly resistant, etc., and then current starts straying and returning on one of the unintended/undesired ground electrical paths between the buildings!



I keep forgetting that 4-wire feeds weren't always the norm or code... : / But regardless of code, 4-wire feeds are always safer than their 3-wire counterparts!

And tamper-resistent outlets and AFCIs are now the norm and are "safer" as well. That doesn't mean that houses without them are substantially less safe.

Everything in the NEC provides different levels of safety. This is a very MARGINAL one. Having GFCIs in your bathroom and kitchen are BIG ones. Others are marginal and theoretical and don't really play out IRL.

 

[wyliesdiesels]

IMHO, I don't believe the 4iwire requirement is a marginal safety measure. I have seen electrical systems that had return current on undesired metal paths between buildings! Yes, I know there's millions of electrical systems wired the old way but when I do electrical for clients, I always like to make sure it will be safe. When it comes to a 3-wire feed vs. a 4, yes the majority of 3-wire feeds out there will probably never have this issue.

But the point of code is to do things a certain way to prevent something bad from happening NOT if it ever will! Take for example feeding a 14ga NM wire with an over rated breaker. Now, the normal load on the wire(say a well pump), only draws 5a FLC, so the wire is fine. But say a line to line short happens some where along the line, causing the wire to be overloaded and possibly starting a fire. The wire should have been protected with a 15a breaker to prevent the preceding hypothetical scenario even though that situation would probably never happen!

 

[Aceman]

But the point of code is to do things a certain way to prevent something bad from happening NOT if it ever will! Take for example feeding a 14ga NM wire with an over rated breaker. Now, the normal load on the wire(say a well pump), only draws 5a FLC, so the wire is fine. But say a line to line short happens some where along the line, causing the wire to be overloaded and possibly starting a fire. The wire should have been protected with a 15a breaker to prevent the preceding hypothetical scenario even though that situation would probably never happen!

Wylie, that is a poor example.

There is a difference between an overload, short circuit and ground fault. Saying a 15 amp breaker would always trip faster with a short circuit than a larger breaker simply isn't true.

 

[Charles (in GA)]

And tamper-resistent outlets and AFCIs are now the norm and are "safer" as well. That doesn't mean that houses without them are substantially less safe.

Everything in the NEC provides different levels of safety. This is a very MARGINAL one. Having GFCIs in your bathroom and kitchen are BIG ones. Others are marginal and theoretical and don't really play out IRL.

Indeed, tamper resistant receptacles in my house with myself and my cat would be absurd. Last time there was a small child in the house was a number of years ago when my brother/wife/niece were here to visit. My niece is 15 now, has a drivers license and sports about town in ND on her own, she won't go sticking anything in a receptacle except the charger for her ipod.

Charles

 

[wyliesdiesels]

Wylie, that is a poor example.

There is a difference between an overload, short circuit and ground fault. Saying a 15 amp breaker would always trip faster with a short circuit than a larger breaker simply isn't true.

O ok. I didn't know a breaker would even know the difference. I guess we're getting into electrical engineering now.....

 

[pattenp]

Wylie, that is a poor example.

There is a difference between an overload, short circuit and ground fault. Saying a 15 amp breaker would always trip faster with a short circuit than a larger breaker simply isn't true.

I’m not too sure I agree based on my understanding. An overload and a short circuit are two different terms for describing the occurrence of over current that trips a breaker. But the mechanics that take place within the breaker is the same. A short circuit causes an over current that exceeds the breakers designed limit which in turn trips the breaker. So a breaker designed to trip at 15A in theory should trip a nanosecond quicker than the 30A on a short.

 

[Falcon67]

The reason code was changed was because of safety. The issue arises when there are parallel electrical paths between buildings(water line, gas line, etc.) and the intended return path(neutral wire) becomes disconnected, corroded/highly resistant, etc., and then current starts straying and returning on one of the unintended/undesired ground electrical paths between the buildings!



I keep forgetting that 4-wire feeds weren't always the norm or code... : / But regardless of code, 4-wire feeds are always safer than their 3-wire counterparts!

I don't have anything here at work to reference, but I seem to recall that one of the requirements that allowed the older 3 wire feed was that there had to be absolutely no other paths between the buildings, period. No phone, cable, water, gas, etc - nothing.

 

[wyliesdiesels]

I’m not too sure I agree based on my understanding. An overload and a short circuit are two different terms for describing the occurrence of over current that trips a breaker. But the mechanics that take place within the breaker is the same. A short circuit causes an over current that exceeds the breakers designed limit which in turn trips the breaker. So a breaker designed to trip at 15A in theory should trip a nanosecond quicker than the 30A on a short.

Ok, cool, so I'm not the only one who understood it this way....yeah I thought a short circuit, overload and a ground fault were all seen by a breaker as the same thing- an overload!

I don't have anything here at work to reference, but I seem to recall that one of the requirements that allowed the older 3 wire feed was that there had to be absolutely no other paths between the buildings, period. No phone, cable, water, gas, etc - nothing.

Yeah, that may have been the original requirement for a 3 wire feed to be allowed. The feeder feeding my garage would fail this code miserably! Its a 14/2 UF feeding a small subpanel which powers a well pump and 2 garage circuits! So the EGC is being used as the neutral and there is no ground rods....I only rent and the landlord thinks there's nothing wrong with it, so it aint gonna get fixed... :/

 

[ishiboo]

Ok, cool, so I'm not the only one who understood it this way....yeah I thought a short circuit, overload and a ground fault were all seen by a breaker as the same thing- an overload!

Not quite.

Both a short circuit and overload may trip a breaker through the same mechanism, but an overload is typically a MUCH smaller amount. A short circuit can easily generate several hundred, thousand, or even tens of thousands of amps for a short period of time. This is where the breaker's AIR rating comes in - completely different than it's thermal protection rating. The breaker needs to be able to quickly interrupt these huge loads before it gets welded together and all the wiring along the way vaporizes An overload heats up the breaker's thermal trip slowly, and the breaker will handle small overloads over time.

Ground faults are rather completely different. Many/most ground faults will not trip a typical breaker at all. Your smallest breaker is usually a 15A... based on several factors it will actually trip at different currents, but not below <15A.

A GFI can easily pick up a 4ma current leak (ground fault) and trip. It would take over 3700 times this current at a MINIMUM to trip the breaker (actually far more, again depending on the breaker's actual trip curve) under what a normal breaker is designed to do - over current and short circuit protection. And it would take some time to do this! A typical circuit breaker has no idea that the current is not traveling back on the intended path, so unless the ground fault exceeds its thermal overload rating it will not trip and it will think its a completely normal load. GFIs also have a bit of a different switching mechanism in them than a circuit breaker.

 

[ishiboo]

I’m not too sure I agree based on my understanding. An overload and a short circuit are two different terms for describing the occurrence of over current that trips a breaker. But the mechanics that take place within the breaker is the same. A short circuit causes an over current that exceeds the breakers designed limit which in turn trips the breaker. So a breaker designed to trip at 15A in theory should trip a nanosecond quicker than the 30A on a short.

They are and they aren't. An overload is typically gradual heating and highly dependent on the breaker's trip curve.

A short will be MUCH higher amperage and will tend to trip a 15, 20 or 30A breaker at practically the same time - which is much faster than a small thermal overload.

Because of the physics involved in interrupting a very high amperage short, the breakers are designed and rated just for this purpose even though the mechanism is the same for both uses in home circuit breakers.

 

[toler234]

the only place the ground and neutral are bonded is at the meter, everything on the load side needs to be 4wire, and neutral and grounds are on separate bars

 

[wyliesdiesels]

Not quite.

Both a short circuit and overload may trip a breaker through the same mechanism, but an overload is typically a MUCH smaller amount. A short circuit can easily generate several hundred, thousand, or even tens of thousands of amps for a short period of time. This is where the breaker's AIR rating comes in - completely different than it's thermal protection rating. The breaker needs to be able to quickly interrupt these huge loads before it gets welded together and all the wiring along the way vaporizes An overload heats up the breaker's thermal trip slowly, and the breaker will handle small overloads over time.

Ground faults are rather completely different. Many/most ground faults will not trip a typical breaker at all. Your smallest breaker is usually a 15A... based on several factors it will actually trip at different currents, but not below <15A.

A GFI can easily pick up a 4ma current leak (ground fault) and trip. It would take over 3700 times this current at a MINIMUM to trip the breaker (actually far more, again depending on the breaker's actual trip curve) under what a normal breaker is designed to do - over current and short circuit protection. And it would take some time to do this! A typical circuit breaker has no idea that the current is not traveling back on the intended path, so unless the ground fault exceeds its thermal overload rating it will not trip and it will think its a completely normal load. GFIs also have a bit of a different switching mechanism in them than a circuit breaker.

Ok, that makes sense. I learned something today. Thank u for the 2 explanations. I've read briefly on AIR ratings but didn't quite know how they applied. Guess I should've read up more on AIRs!

the only place the ground and neutral are bonded is at the meter, everything on the load side needs to be 4wire, and neutral and grounds are on separate bars

And don't forget that the neutral bar needs to be isolated/insulated from the panel enclosure!