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Old 01-17-2009, 10:22 AM   #1
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Panel History (old Breaker Panel Question)


Where there older panels that were produced with isolated neutral / ground bars? (when did they first produce a mass market panel that had isolated bars in it)

I was under the impression that in general it was only fairly recently (last 10 or 15 years) that there was a isolated bar installed in most panels and prior to that the bar or bars were permanently bonded to the box.

Any idea when including an isolated bar became the norm?

A EC was out 2 days ago, and told my dad that he wasn't sure if the ground bars in his panel were bonded (it is a fused main CH panel from the early 1960's). Were there any panels made around there that had isolated bars?

The guy also grabbed the service neutral with his bare hands while the panel was live. Do you guys touch a live service neutral, it's current carrying, so if he was grounded, why couldn't he have gotten shocked? I did take a reading from the service neutral to the ground wire and didn't read any voltage.

I was sure the bar was bonded. I put my Ideal RMS meter on the bar and the box and had virtually no resistance reading.

Thanks

Jamie
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Old 01-17-2009, 11:20 AM   #2
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Panel History (old Breaker Panel Question)


The code has specified for a very long time that the neutral and ground be separated if it isn't the first means of disconnect. I'm sure that panels would have to have had an isolated neutral in installations where the panel is downstream from a disconnect.

Why couldn't your electrician tell if the ground was bonded? It is a matter of locating the bonding jumper, either strap or screw, that connects the neutral with the panel enclosure. And as you did, a continuity test between the two.

As far as grabbing a current carrying neutral, well, it depends on the voltage drop on that neutral. If the neutral is heavily loaded and you have a large voltage drop, then a current could flow from it to ground, but it would be small. A matter of a couple of volts won't even be noticeable to a person. Any more than that and you likely have a bad neutral connection.
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Old 01-17-2009, 11:24 AM   #3
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Panel History (old Breaker Panel Question)


Most breaker boxes from 40 years ago and possible more have had their neutral bars mounted on insulated spacers.

Many of the older fuse boxes did not.
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Old 01-17-2009, 03:27 PM   #4
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Panel History (old Breaker Panel Question)


Why couldn't your electrician tell if the ground was bonded? It is a matter of locating the bonding jumper, either strap or screw, that connects the neutral with the panel enclosure. And as you did, a continuity test between the two.

I don't know, I wasn't talking to the guy. My dad was impressed with the guy, but them my dad told me what he said about not knowing if it was bonded or not. Then the electrician told me dad that if it wasn't bonded that's probably why all the damage occurred.

I think it is bonded under the main breaker, and he probably didn't want to pull the main. But I don't know why he could not have used a meter.

My pushmatic panel from 1963, which would have been install around the same time as my dads CH panel, appears to be permanently bonded to the box with no isolation.

As far as grabbing a current carrying neutral, well, it depends on the voltage drop on that neutral. If the neutral is heavily loaded and you have a large voltage drop, then a current could flow from it to ground, but it would be small. A matter of a couple of volts won't even be noticeable to a person. Any more than that and you likely have a bad neutral connection.

This guy (electrician without a meter) had no way of knowing what the load was or if the neutral was bad. I wonder why this guy didn't exercise a bit more care...

Now with a clamp meter, I should see the difference in the unbalanced load, just like I would see on a MWBC, right?

Thanks
Jamie
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