Today I asked for a quote on a 400A 2-gang meter socket with disconnects. What I got was a quote on a 400A 2-gang meter socket with (2) 200A breakers in each section. I was told that feeding a 400A MLO panel with (2) 200A paralleled breakers was OK. These breakers operate independent of each other and are factory installed in the meter socket section.

I have never come across this set-up before. According to 240.8 it seems to be OK. It just doesen't sound right to me.

Have any of you guys done this or seen this done before?

Brian

If I am understanding this set up, I would be worried about keeping the neutrals seperate between the services. Or if they are truly parallel I would think this would only have a 200 Amp capacity before tripping.

Your right, it does not sound right.

Sounds like 2 200a panels from that, not a single feed at 400a from it...... Unless they are linked in some way? Many class 320/400 resi services are like that.

From the commentary of 240.8

Either way it sounds odd that a 400A 2-gang meter socket would have 4 200a CB's.... 800A of combined protection with no diversity on a 400A meter?

Got a model and make?

It would be a GE meter socket. He was supposed to email a cut sheet.

You guys are right. What would keep someone from using (4) 200A breakers for a 800A subfeed?

I thought about the (2) 200A panels. I have to run the numbers to see if would be cheaper.

As it stands. The parallel breaker set-up is about $1000.00 cheaper than a single 400A main.

Brian

At 200A CB's change dramaticaly in class, and frame.

Ya, two 200A breakers are going to be around $1000 cheaper than one 400A breaker. Once you get past 200A, the price goes up pretty close to exponentially with ampacity.

If the documentation with the equipment says that it's intended for a 400A feed, then it's OK. But, I think the chances are upwards of 90% that this setup is intended to feed two 200A MLO panels, and isn't listed to feed a single 400A panel.

[This message has been edited by SolarPowered (edited 06-30-2006).]

Two 200 amp over current devices in parallel will provide 400 amps of capacity.

You don't parallel breakers perod, or LV fuses that I am aware! You can discuss if in theory all that you want but it can not be applied.
The only area where I have see fuses paralled is in medium voltage application where a specific fuse holders have been provided and ratings has been given for the combination.

Dave you are correct we can not parallel OCPs in the field. However some equipment comes that way.

My 200 amp GE service panel uses four single pole 100 amp breakers with two in parallel to provide two legs of 200 amp capacity.

I also find fuses in parallel in some equipment.

My point was it works although it is generally an NEC violation.

Bob

Yesterday I called Tim Croushore of Allegheny Power. Tim is or was on a Code making panel (Don't know which one but his name is in the code book).

After I explained the situation he agreed that parallel breaker would not be compliant in this situation. He said that if the breakers were installed in the panel feeding a split buss it would be OK. That was not my case.

I told the supplier. The supplier wanted to get more info. He did say again that he has sold this set-up before and it was passed.

We'll see where this goes but we all learned something. I love it when that happens!

Brian

From an engineering standpoint, it doesn't seem to be much of a power risk- if one of a paralleled breaker pair trips from an overload, the other will trip in turn, regardless of whether they're yoked together or not. And it's impossible to overload the cabling. Really, I think this makes more sense than paralleling transformers, as there is less risk of a damaging overcurrent fault.

As to whether they come like that at the factory or not, that seems kinda BS. So long as you can retrofit a yoke, I see no problem- that was the only way we ever did it on naval ships, we'd buy the individual breakers and then a 2x or 3x yoke depending if it was a "1-phase" or 3-phase circuit. I really fail to see how it could make a difference being factory or field assembled. I wonder if there were problems in the past with improper field assemblies that precipitated this?

I would never dream of doing such a thing unless you were locking the handles together. Otherwise, unless the breaker characteristics were exactly the same, one might trip first. If the O/L cleared before the 2nd breaker tripped, you would have a 200A feed until someone noticed or the next O/L. If it was for a split feed, they wouldn't be parallel. Also, could you be absolutely sure that each breaker was flowing 50% of the load?
Joe

Joe is absolutely right! there is no way to guarantee that the load will always equally divide itself between the two fuses or breakers.

Of course he is right the current will never divide perfectly evenly.

However it will divide evenly enough not to matter in the least assuming the circuit is reasonably identical.


Again I am just pointing out it works and many manufactures take advantage of this.

I do agree in regards to the opening post it is wrong and he needs a single 400 amp device.


Without a doubt one will trip first.

I would like to know how the other would not open fairly quickly at over 200% it's rating and if it did not open the safety hazard that would create.

Iwire:
Of course he is right the current will never divide perfectly evenly.

I would like to know how the other would not open fairly quickly at over 200% it's rating and if it did not open the safety hazard that would create.


So if we consider the possibility of uneven loading, even 2 breakers with identical curves, would be operating at different points on their curves. So the O/L condition might be trailing off as the first breaker is tripping. The 2nd breaker wouldn't trip. Now you have a 200A service instead of 400A and wouldn't know it. I don't see it as a safety hazard as much as a nuisance. But why wouldn't you tie them together if you were going to use them in place of 1 breaker? Can you imagine how tightly individual breakers would have to be inspected to ensure a match along the entire curve? Considering I just got an Agastat that didn't have its mounting holes tapped, I don't think I have that much confidence. User adjustments on the breakers would make things really interesting.
Joe



[This message has been edited by JoeTestingEngr (edited 07-01-2006).]

Joe I think your grasping at straws.

That is as likely as me hitting the lottery.

Bob

Just for fun, most thermal mag breakers will begin to open @ approx. 1.1 x handle rating in 1000 seconds. @ 2 x handle rating in 20-40 seconds.
That would be continuous load for the time period. Would a residential service see 400A load for >20 seconds to activate the thermal trip? It's got to be a big house.

Joe I think your grasping at straws.
That is as likely as me hitting the lottery.
Bob

Bob, I think that you are either:
1.) Overly optimistic of installation variables.
2.) Overly optimistic of manufacturing tolerances.
or
3.) Overly optimistic of your chances of winning the lottery.

The only advice I can offer is that you should either:
A.) Tie the breaker handles together
or
B.) Fill all of the balls that you don't want with a liquid to weigh them down.

Both of these methods have proven highly effective in the past. I suggest the former because a famous bowling and movie host in Pa. went to jail for the latter.

What I guess I don't understand is this: You claim that you are saving a thousand bucks using two breakers as one. Why then not spend a small fraction of that to guarantee that they function as one. A simple handle would eliminate a large number of variables.

I've never dealt with a case of parallel breakers. I can't pretend to know all of the possible conditions and variables. Part of my job is to deal with as many of the "what ifs" as i can discern. What if, for instance, these breakers have ground fault settings. Again, I don't know. One could trip on a non-overload. You wouldn't know.

It has been mentioned before that I might view things differently as a Testing Engineer. This is true but I think that it is more because I have been trained as a pilot and skydiver. We are drilled over and over and over to respond to emergencies that have a whole number zero percent chance of happening to us. But yet, every emergency we train for has taken human lives so we train. We carry a reserve on our backs, worry about best glide and balanced field lengths, tie our breaker handles together, and spend our lottery money on lift tickets.<G>
Joe

Fair enough Joe we can once again disagree.

This for me has been strictly something for discussion.

I will now remove my GE service panel and send it to GE with a note that says "Joe says it won't work".


I am not optimistic about either of those, I am counting on the fact the breakers will have different characteristics.

2 - 200 amp breakers in parallel supplying one feeder.

The load on the feeder some how goes above 400 amps.

The first breaker trips leaving the remaining breaker to hold the load which would still be over 400 amps.

This second breaker no matter how far out of whack from the first is going to trip quickly with 200% or more of it's rating passing through it.

Now lets say the planets where perfectly aliened and for some reason just as the first one tripped the current dropped from more than 400 amps to less than 200 amps just at the right moment leaving us with a '200 amp feeder'

All that has happened is the power stayed on perhaps to trip out on another day.

The level of inconvenience seems the same.

Do you work with building wiring systems?

I ask because you seem to look at it like building a fine watch when in reality it is a fairly crude process when dealing with typical inexpensive molded case circuit breakers.



Handle ties do not ensure both breakers will open on a 'trip'. Handle ties only ensure manual operation is simultaneous.

This is a result of breakers 'trip free' design.

I will see if I can post a picture of my GE panel.

I also never said I would do this, it is an NEC violation to do this in the field.

Bob

Bob, I think I'll just agree to agree with you. You wouldn't do it, I wouldn't do it, and the NEC doesn't condone it. I see your point about the trip free aspect. I was just thinking of how I have never had a two pole breaker trip one half of the assembly. My building wiring system experience has been bus maintenance and transportation facilities, rail maintenance and yard facilities, passenger stations and traction power substations. There's lots of misc. stuff thrown in there too. In all of these locations, I have not seen parallel breakers. This is a concept that I had never given any great consideration to until this thread.


"I will now remove my GE service panel and send it to GE with a note that says "Joe says it won't work"."

How about just sending them an Email inquiring as to reports of only one breaker tripping?
Joe

Let me just add that I may have seen panels constructed this way and not realized it. I don't typically ask electricians to take panel covers off to examine the bus work. I do deal with many split panels with lighting contactors and the like.

[This message has been edited by JoeTestingEngr (edited 07-02-2006).]

If my last post seemed harsh cut me some slack I am taking pain killers. (Prescribed)

Anyway


Would they tell me?

After some thought I think there is a good chance that my GE breaker has an internal common trip bar.

Thanks for letting me have one.

Bob

Bob, I was told by a GE engineer that those 4-section GE main breakers consist of a 2-pole 100a breaker paralleled by a pair of non-current-sensing contacts in the outer cases, solely for the purpose of lower overall contact resistance.

I'll do more than that Bob. I'll offer up my prayers that you're soon healed of whatever's troubling you! I really enjoy your posts, the give and take. This has been a very educational experience and I thank you for your part in it.
Joe

Thanks Joe, it's nothing serious but the meds make me a bit cloudy.

Larry they can justify anyway they want.

IMO it is strictly an issue of 'value engineering' what they did costs less than a 200 amp case breaker.

One advantage to the use of double breakers in a loadcenter is the ampacity of the bus connection. By keeping each stab to 100A max they can plug on a larger breaker without having to make a special bus connection and then there are on bolts to tighten.

We use completely separate (non-yoked) parallel breakers all the time for redundancy. Example: Parallel-Redundant UPS system. Also, N+1 generators: each gen has its own output breaker. This is all allowed under NEC and works well in practice, too. EXTREMELY well, too, as in 99.999-99.9999% reliability well. In the case of the generators, they have integrated governer and droop-adjusting circuitry to maintain proportionate load, but the UPSs maintain even load, even in bypass. In a properly cabled system, minute differences in breaker manufacture and cable installation don't amount to much of a current split difference. And if one breaker should trip while the other somehow miraculously doesn't? Alls the better, as you have time to fix the first UPS!

Care has to be taken with interlocks (both key-type and PLC) when multiple switchboards are used, to prevent the branch circuit from becoming a bus tie, but otherwise, it's pretty straightforward.

[This message has been edited by SteveFehr (edited 07-03-2006).]

Steve, You're describing multiple sources with output breakers feeding some sort of reliable or emergency bus. That is apples & oranges to what we are talking about. Now, if one of your UPSs or Gensets had 2, 200A output breakers, instead of 1, 400A output breaker, we would be on the same page.
Joe

JBD


I agree I bet that has a lot to do with it.

SteveFehr

I am familiar with the systems you describe and I have to agree with Joe, that is different set up entirely.