Shunt trip physical design

[RossS]

Sorry if this repeats an earlier post. I tried to find an answer in the forum, but a search on "shunt trip" produces hundreds of hits - this forum is HUUUGE!

Is shunt trip breaker design standardized?

In doing a design I have to balance my panel loads, or at least total them up. Shunt trip breakers have been a bit of a dilemma. At least for lower amperage breakers, the shunt trip breaker uses an extra slot, or pole (I've taken to calling it the "shunt pole"), in the panel, but doesn't electrically connect to that pole. I need to know which side of the breaker the shunt pole is on. That is, if a shunt trip single pole 20A breaker is installed in the very top left of the panel, is the load on the A phase (slot 1) or on the B phase (slot 2)?

I asked my Eaton rep this question and this is what I was told regarding Cutler Hammer's shunt trip breakers:

(Large case breakers, 3P100 and above, do not require an extra space). For the smaller breakers, the shunt pole is on the bottom when the breaker is installed on the left side of the panel.

But my problem is that I've only actually seen Square D breakers, and they're exactly the opposite. In fact, I found a picture of one elsewhere in this forum, and it illustrates it perfectly.

So, did my Eaton Rep not understand the question, or does the design vary from manufacturer to manufacturer?

Thanks

 

[iwire]

I don't think there is any standard.

Consider that each manufacturer is free to design how the breaker mounts to the panel why would they be forced to place the shunt on one end or the other?

 

[benaround]

RossS

It won't really matter if they are on top or bottom, if they are on the same

side of the panel every third breaker will be the same phase. If circuit is on top

and shunt is on bottom, it will be--A,C,B,A,C,B---flip flop them--B,A,C,B,A,C

 

[mdshunk]

In some panels, you can move the bus fingers around, and buy special fingers for certain things. This can make balancing things out a bit easier.

 

[RossS]

Thanks

Thanks

Thanks all:

That's what I was afraid of, no standardization. Any knowledge of how NEMA approaches this type of situation? Are there channels for making the case for standardization?

Benaround, I don't think you fully understood my dilemma.

What you said is true if I'm dealing with 3 phase loads; it only becomes an issue when I have larger single phase loads. Then the exact phase loading matters when I submit a design for permitting. The AHJ's around here (not to mention just good engineering practice) require the phases be reasonably balanced and no single leg exceed the panel rating. It becomes challenging when trying to squeeze a 398A restaurant service into a 400A panel (knowing full well that the clients don't want to pay for a 600A service if they don't have to). If I spec a CH panel and assume the EC will provide CH breakers, and then it turns out the EC provides Square D without checking with me (which we know they would never do), then my calculations will be off (because apparently CH and SD design their shunt trip breakers differently), and in the situation I've described, I'll probably have a leg that's over loaded, at least on paper. And if I have say, 41 circuits in a 42 circuit panel, moving them around to rebalance the load will most likely be challenging and may not even be possible. Even if it is possible, the panel schedule will have to be reworked, the diversified load recalculated, the homeruns relabelled (with a lot of opportunity for error) - all in all, a significant amount of work that I might not get paid for and that I'd love to be able to avoid.

I'll be covered contractually, but my client will be PO'd and will think, because it's electrical, that I'm to blame. Regardless of blame, I'll still probably be the one that will get to fix it.

We all know that if you check meter a service it almost never meters out to what's calculated, plus - hopefully - there's enough diversity built into the code requirements that it won't matter. Still, when I'm trying cover my butt from a liability standpoint, it can be dicey, and I want to make sure I cover each possible contingency with a good CYA note.

Thanks again all,
Ross

 

[LarryFine]

Ross, wouldn't careful initial breaker placement, with half of the shunt-trips on each side of the panel, still allow even line loading? Whether the shunt half of the breaker case is 'above' or 'below' the active half shouldn't matter if they're split side to side.

 

[Jraef]

Thanks all:

That's what I was afraid of, no standardization. Any knowledge of how NEMA approaches this type of situation? Are there channels for making the case for standardization?
...snip

Thanks again all,
Ross

NEMA would not be involved. Panelboards and Load Centers are not designed to be interchangeable from one manufacturer to the next, so as was mentioned above, every mfr. can do what they want in terms of a design; it only applies to THEIR products. In general, Shunt Trip breakers are rare, i.e. you might find one or two in a panel sometimes, so I doubt anyone considered a situation where circuit balancing would be seriously affected like this.

I would advise picking one manufacturer and insisting on it specifically, then put in the onus on the EC to take design responsibility if they decide use something different.

 

[Keri_WW]

I've designed a few dining facilities and have always based my design off of Square D. Each one was returned with submittals for Eaton products. I balance the best I can while designing, and its usually fairly simple to balance the panels that have shunt trips in them. That being said I've yet to encounter any problem with having the contractors install Eaton vs. SD. For larger facilities those loads/panels are pretty insignificant to the overall loading.

 

[RossS]

Larry:

Your suggestion works reasonably well, and when it does work, that's what I do. (For perfect balancing the loads would have to be identical, but they're usually close enough.) And normally I'm only dealing with only one to three, maybe four electrical devices under a kitchen hood.

Like I said, it only comes up when I'm maxing out a service both in terms of ampacity as well as circuit count and I'm trying to avoid moving up to the next larger service. So that means it doesn't come up often. But when it does, it's a royal pain in the neck.

 

[Keri_WW]

Like I said, it only comes up when I'm maxing out a service both in terms of ampacity as well as circuit count and I'm trying to avoid moving up to the next larger service.

Don't you think you are doing your client a disservice by not leaving them room for future capacity/growth? Sure you save them a decent chunk up front with a smaller service, but I can guarantee you that the cost will be exponentially higher years down the road. :grin:

My firm tends to design with 20-30% spare capacity for future growth (dependent on the building type, clients demands, etc).

 

[LarryFine]

Larry:

Your suggestion works reasonably well, and when it does work, that's what I do. (For perfect balancing the loads would have to be identical, but they're usually close enough.) And normally I'm only dealing with only one to three, maybe four electrical devices under a kitchen hood.

Wow, it didn't hit me that you were talking about kitchen hood systems. I've been doing a good number of them lately, and I love doing them. We should talk. PM me for my number if you want to, or PM me yours. (Don't worry, I'm not a weirdo.)

Like I said, it only comes up when I'm maxing out a service both in terms of ampacity as well as circuit count and I'm trying to avoid moving up to the next larger service. So that means it doesn't come up often. But when it does, it's a royal pain in the neck.

You might consider using a sub-panel supplied by a single shunt-trip in the big panel, or even a contactor or few for appliances. I've found them to be more economical than shunts, but I will certainly use them when they're there.

I should mention that many of the system I wire are older existing hoods that may have never had the fans connected, or a mechanical gas valve is being replaced with an electric one. In any case, none of them meet present requirements.

Added: Half of the work can be figuring out how the existing system is wired, so I can choose the best way to interface the new stuff with the existing setup.

One good one, for example, had two separate intake blowers and two exhaust blowers (with four individual switches, which they wanted to keep), lights, a new electric gas valve, and a horn/strobe. I only used one microswitch and four contactors.

It's only slightly complicated because, around here, the gas valve must shut off every time the exhaust shuts off, even manually. They have to turn on the exhaust before they can even light the pilot lights. I can tell you, the restaurant guys hate it.

 

[iwire]

(Don't worry, I'm not a weirdo.)

Maybe we should have a poll about that? :grin:

 

[LarryFine]

(Don't worry, I'm not a weirdo.)

Maybe we should have a poll about that? :grin:

Do I get to vote?