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busbar arrangement


John Dirks Jr
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On 120/240 volt circuits such as a clothes dryer we need to verify that the 2 hot feeds are on different bus bars so the neutral wont get overloaded.

I want to know if there is a general way to recognize the busbar arrangement by looking at the breaker/fuse arrangement. I probably had this in training but I need to refresh.

Two questions;

1. Some breaker/fuse panels have two rows of breakers lined up across from each other. Is it "always" safe to assume that each vertical row is on the opposite busbar?

2. On breaker/fuse panels with a single row top to bottom, is it "always" safe to assume that every other breaker in the row is on the same busbar?

The point is, I want to strike up conversation on ideas to identify busbar breaker/fuse arrangement.

Even if the conversation will only lead to, "this brand is this way and that brand is that way", well, lets have it.

Pictures will be helpful too so please post them if you can. A group effort would be nice. Each person could post a picture(s)

of a particular panel arrangement along with an explanation of the layout.

A link(a) to a page(s) with multiple examples would be good too.

Thanks.

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First the only way to obtain 240 is to connect to both "sides" of the incoming current. Either side to the neutral is simply 120. The neutral is not needed to obtain 240.

The handles of the breaker that supply 240 are to be tied together by a factory mechanism. Two breakers on the same plane or vertical placement in a panel are attached to the same portion of the bus bar. You will not get 240.

Go to HD or your local building supply store. You can safely see and touch. I recommend this process to learn more about most any building material, see touch and read the instructions, labels etc. I do not recommend you talk, ask or listen in this enviorment.[:-graduat

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I totally screwed up the question. Sorry. Some 240 appliances still need a neutral though don't they? Like a dryer for instance, the heating element might use 240 but the timer for the control and the light bulb use 120. So therefore, it needs a neutral right?

Sorry I messed up the question and that confused your answer but you are right anyway. I botched it up. Don't know where my head was.

I am aware that the 240 appliance wont even work if it doesn't get the two feeds from the opposite busbars.

Lets change the original question to regard of multi-wire branch circuits instead of a 240 appliance. For example, a kitchen receptacle fed by two hots, each with its own breaker/fuse. If fed by a single 3 wire conductor, those two hots need to be on opposite busbars to prevent the neutral from being overloaded.

This is an example where making sure the two hots need to be on opposite busbars and that is the reason I wanted to discuss breaker/fuse and busbar arrangements.

I confused the issue enough already it may never get on the right track. I mean a 120v receptacle fed by two hots with a 3 wire conductor using 1 neutral. Get the picture?

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"Lets change the original question to regard of multi-wire branch circuits instead of a 240 appliance. For example, a kitchen receptacle fed by two hots, each with its own breaker/fuse. If fed by a single 3 wire conductor, those two hots need to be on opposite busbars to prevent the neutral from being overloaded."

The very reason to count the neutral wires and compare the count to the number of breakers.id="blue">

"I mean a 120v receptacle fed by two hots with a 3 wire conductor using 1 neutral. Get the picture?"

The breakers should be on different bus bars. They would not be next to one another horizontally or vertically.

Get what picture?id="blue">[;)]

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Originally posted by fqp25

When is one 120V receptacle fed by two hots?

As for 3 wire conductor with 2 hots???? - Except for power cables for 220V appliances, don't they usually have a hot, neutral, and ground?

Read up here

http://www.inspect-ny.com/electric/multiwir.htm

The intent of the post was to discuss breaker/fuse layout with respect to their relation to the two different busbars. I screwed it all up from the beginning.

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Originally posted by AHI

1. Some breaker/fuse panels have two rows of breakers lined up across from each other. Is it "always" safe to assume that each vertical row is on the opposite busbar?

2. On breaker/fuse panels with a single row top to bottom, is it "always" safe to assume that every other breaker in the row is on the same busbar?

Just the opposite. Every other breaker is on an opposite busbar, no matter if the breakers are lined up horizontal or vertical, one row or two.

Charlie has some good advice; go look at the equipment in a different environment.

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Originally posted by Neal Lewis

Originally posted by AHI

1. Some breaker/fuse panels have two rows of breakers lined up across from each other. Is it "always" safe to assume that each vertical row is on the opposite busbar?

2. On breaker/fuse panels with a single row top to bottom, is it "always" safe to assume that every other breaker in the row is on the same busbar?

Just the opposite. Every other breaker is on an opposite busbar, no matter if the breakers are lined up horizontal or vertical, one row or two.

Charlie has some good advice; go look at the equipment in a different environment.

Are you sure? Look at the photo in the link I posted above. He is pointing at two breakers seperated by another that is in between them. He is indicating that it is wired wrong because they are on the same busbar. This suggests that every other breaker on the panel in this particular photo is on the same busbar.

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What I do with 240 Volt 3 and 4 prong female receptacles is test the two hot lines for 240 Volts and check each hot line to ground and to neutral (if one exists). I use one of those little 120/240 Volt 2 probe units with LEDs. No need to worry about bus bars in this instance since they will have to be on separate bus bars to get 240 Volts to begin with across both hot lines.

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Originally posted by msteger

What I do with 240 Volt 3 and 4 prong female receptacles is test the two hot lines for 240 Volts and check each hot line to ground and to neutral (if one exists). I use one of those little 120/240 Volt 2 probe units with LEDs. No need to worry about bus bars in this instance since they will have to be on separate bus bars to get 240 Volts to begin with across both hot lines.

I would have to agree this is the fastest way to do it at the receptacle end, but you must still make sure that breaker handles for split receptacles are mechanically linked in the panel for safety.

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John,

The single most common defect regarding your question is the use of wafer/ space saver breakers. If a space saver breaker is used in a MWB circuit then the neutral carries the sum of the loads rather than the difference of loads.

The most common place a problem like this is evident is the dishwasher/ disposer circuits being fed to a duplex receptacle through a MWB circuit "protected" by space saver breakers.

The neutral is almost always the color of toast.

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Good point, Alex. I should have also mentioned breaker tie handles. I always also make sure proper breaker tie handles are installed. I am sure we've all seen nails or copper wire used to mechanically tie two breakers together. Only proper breaker handle ties are to be used for mechanically tying two breakers together for a 240 Volt circuit. The wafer breaker issue is a good point, Chad!

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This suggests that every other breaker on the panel in this particular photo is on the same busbar.

That is correct. They are. If he joined either of the ones he is pointing to to the middle breaker he could create a 240v circuit because two side by side breakers on the panel are on separate buss bars. Go to Home Despot and spend some time in the electrical department looking at boxes and how they are set up.

P.S. I hope your reports are more clearly understood than your questions.

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Originally posted by AHI

. . . I want to know if there is a general way to recognize the busbar arrangement by looking at the breaker/fuse arrangement. I probably had this in training but I need to refresh.

Two questions;

1. Some breaker/fuse panels have two rows of breakers lined up across from each other. Is it "always" safe to assume that each vertical row is on the opposite busbar?

No. Don't assume. Get a tester and touch it to the lugs. Then you'll know.

2. On breaker/fuse panels with a single row top to bottom, is it "always" safe to assume that every other breaker in the row is on the same busbar?

Nope. Zinsco/Sylvania are impossible to tell.

Get a tester. Use it.

- Jim Katen, Oregon

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Originally posted by AHI

Jim,

Please explain exactly how to determine opposite/similar busbars using a tester.

What kind of tester? VOM?

Thanks

You can use a Wiggy, a multi-meter or a plain two-lead neon tester such as a Detect-o-lite. Anything that will read 120 volts vs. 240 volts vs. 0 volts.

Place one lead on one breaker terminal and place the other lead on the other breaker terminal. If your tester says 240v, then the breakers are on opposite busbars. If the tester says 0 volts, then the breakers are on the same busbar.

I've met several electricians who do this test with their fingers. I do not recommend this method.

- Jim Katen, Oregon

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Originally posted by randynavarro

Originally posted by Jim Katen

I've met several electricians who do this test with their fingers. I do not recommend this method.

- Jim Katen, Oregon

Ummmm.. . . Are you serious?

Yes on both points. They did it and I don't recommend it.

Many years ago, I met an electrician in NYC who was, at the time, in his 80s. He said that, as a young man, he'd known Thomas Edison. This old gaffer still went out on service calls. To test for power, he'd grab wires -- I don't mean that he'd brush them with the tips of his fingers, I mean he'd latch onto them and hold on for several seconds while saying stuff like, "It feels like the power's running a little high today."

- Jim Katen, Oregon

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Thanks Jim,

I am using a Sperry DS-500. I experimented on my fuse panel and the method was easy. Mine is a 1962 FPE fuse(not breaker) panel with two side by side rows of 5 breakers each plus a pull out intended for a 240. Each five on either side are on opposite busbars.

Heres something interesting. I noticed that with only one lead of the tester touching a lug and the other hanging loose in the air I got about 10v. I then touched the loose lead to the block wall and the reading came up to 16v.

Heres the kicker that might surprise some people. There is a stack of tires next to the panel sitting on the concrete floor. I touched the second lead to the one of the tires and the voltage jumped to 100.

Go figure. Who would think that rubber tires would be a better conductor than the block wall? What gives? Is it the carbon content in the rubber that works as a conductor?

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Go figure. Who would think that rubber tires would be a better conductor than the block wall? What gives? Is it the carbon content in the rubber that works as a conductor?

Yes.

It ( carbon black colorant) was also responsible for a rash of radiator failures in the mid eighties on GM cars with bad body grounds. Electrolysis literally moved the material in the radiator to the engine blocks.

Most commercial vehicles like police cars and OTR trucks have silicone based hoses to avoid the problem.

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