ICCB vs MCCB vs BPS

[malachi constant]

I'm picking a main for a commercial building. What would you go with and why?

Details: 1600A 208V 3P 4W. All my downstream devices will be fused switches. In the past I would have gone with a BPS but the more I read about their history of spectacular failure (when not maintained) the less inclined I am to use them.

Thanks!

 

[Jraef]

Typically the decision would be inclusive of a fault coordination study.
In layman's terms:

You want a fault to be cleared at the lowest level possible. The "Main" is essentially the last line of defense because if it trips too soon, you lose everything. So typically you want your main to be able to survive lower level fault currents longer than downstream devices so they can have a chance to do their job (reaction time + clearing time). That is the difference between an ANSI C37 ICCB and a UL489 MCCB, the ANSI C37 spec calls for a longer short-time rating.

Disconnects, including Bolted Pressure Switches, are not fault clearing devices, they rely upon the fuses to clear. While it's true that fuses can typically provide higher interrupting capacity and better current limitation than breakers, if your available fault current is low enough for you to consider an MCCB, then that is obviously not an issue. So in this case the BPS is basically a cheap way out of the requirement for having a main, but it brings nothing to the party and it introduces the possibility of a single phasing condition (let alone the failure issue if not maintained).

 

[zog]

Typically the decision would be inclusive of a fault coordination study.
In layman's terms:

You want a fault to be cleared at the lowest level possible. The "Main" is essentially the last line of defense because if it trips too soon, you lose everything. So typically you want your main to be able to survive lower level fault currents longer than downstream devices so they can have a chance to do their job (reaction time + clearing time). That is the difference between an ANSI C37 ICCB and a UL489 MCCB, the ANSI C37 spec calls for a longer short-time rating.

Disconnects, including Bolted Pressure Switches, are not fault clearing devices, they rely upon the fuses to clear. While it's true that fuses can typically provide higher interrupting capacity and better current limitation than breakers, if your available fault current is low enough for you to consider an MCCB, then that is obviously not an issue. So in this case the BPS is basically a cheap way out of the requirement for having a main, but it brings nothing to the party and it introduces the possibility of a single phasing condition (let alone the failure issue if not maintained).

Very well said Jeff, one option to add is the availibility of arc flash reduction or maintenance switches on most modern trip units. This is one of the easiest and most effective arc flash mitigation solutions and should be considered for all mains.

 

[Jraef]

Very well said Jeff, one option to add is the availibility of arc flash reduction or maintenance switches on most modern trip units. This is one of the easiest and most effective arc flash mitigation solutions and should be considered for all mains.

Good point. I forget that in too many instances. I guess I'm still thinking with my old brain cells.

 

[zog]

Good point. I forget that in too many instances. I guess I'm still thinking with my old brain cells.

I am a conferemce addict, I love new products but they sure are hard to keep up with. Arc flash will not be an issue in the future with arc ressistant switchgear and on board remote racking systems. But by the time that becomes the norm you and I will be retired and sipping Mojitos somewhere warm, I hope.

 

[kingpb]

Arc flash will not be an issue in the future with arc resistant switchgear and on board remote racking systems. But by the time that becomes the norm you and I will be retired and sipping Mojitos somewhere warm, I hope.

Future? This gear has been available for quite some time, it's just that Owner's don't want to pay for it. Europe and other IEC countries use this stuff regularly and have for many years.

When the US wants to start enforcing safety, instead of just talking about it, is when this stuff will be the norm not the exception. Because the death rate is low, so far, enforcing safety requirements are still an after the fact.

There would be a lot more work for all of us, if the industry pushed this issue.

 

[zog]

Future? This gear has been available for quite some time, it's just that Owner's don't want to pay for it. Europe and other IEC countries use this stuff regularly and have for many years.

When the US wants to start enforcing safety, instead of just talking about it, is when this stuff will be the norm not the exception. Because the death rate is low, so far, enforcing safety requirements are still an after the fact.

There would be a lot more work for all of us, if the industry pushed this issue.

Yeah future. I have been working with Arc Resistant gear since my ABB days when we introduced "Safe gear" in 1998 (I think) but seeing it actually in a facility is pretty rare. I think the average age of switcgear has to be around 30 years or so, some new stuff and some stuff I still see from the 1940's. So by future I mean based on the average age of 30 years and the arc resistant gear being available for about 10 it won't be the norm for 20 or more years, which makes me retired.

 

[malachi constant]

Disconnects, including Bolted Pressure Switches, are not fault clearing devices, they rely upon the fuses to clear. While it's true that fuses can typically provide higher interrupting capacity and better current limitation than breakers, if your available fault current is low enough for you to consider an MCCB, then that is obviously not an issue.

I can't say the fault current is low enough for me to consider an MCCB, only because I don't know what that threshhold of considering MCCBs should be. One of the reasons I bring this question up is I'm not familiar with the pros and cons of MCCB and ICCB.

Available fault current is ~90KAIC. Is that too high to go with MCCB?

Budget is a major concern on this project, more so than usual as the CM did a poor job estimating early on and it is biting the whole design team as we wrap it up. A couple thousand dollars isn't going to be a big deal, but ten thousand might.

Space restrictions are also a concern here, but I ~believe~ all of these options will fit in the allowed space.

 

[Cold Fusion]

I can't say the fault current is low enough for me to consider an MCCB, only because I don't know what that threshhold of considering MCCBs should be. One of the reasons I bring this question up is I'm not familiar with the pros and cons of MCCB and ICCB.

Available fault current is ~90KAIC. Is that too high to go with MCCB? ....

90K suprises me. I would guess a 500kva, 2%Z. I've only seen one of those before. The secondary distribution was a problem. The issue is to get the short circuit current down to where the panelboards can handle it and the only impedance you are adding is the conductors from the main to the panelboards.

My first recomendation would be to get the different equpment spec sheets and see what they say. Could be by the time you eliminate all that doesn't meet 90K, there is onkly one left.

Concurent with that, see if the different mfg have any appplication guides.

It's really hard to make any determinations with out having the spec sheets.

cf

 

[Cold Fusion]

...Details: 1600A 208V 3P 4W. All my downstream devices will be fused switches. ...!

... Available fault current is ~90KAIC. Is that too high to go with MCCB?

Budget is a major concern on this project, more so than usual as the CM did a poor job estimating early on and it is biting the whole design team as we wrap it up. A couple thousand dollars isn't going to be a big deal, but ten thousand might.

Space restrictions are also a concern here, but I ~believe~ all of these options will fit in the allowed space.

So you are constrained to a high SCC, short on money, tight on space.

Well, there is nothing wrong with designing to meet, but not exceed, spec. But, when the budget is cut to where you have your name on a marginal design that only has the apperance of meeting spec - that's a bummer.

Something I have never understood is a manager that tells me the budget is short and I have to meet spec anyway. It makes me want to ask, "What part of the laws of God and physics would you like me to suspend?"

I am so glad I don't work for commercial morons.

cf

 

[zog]

Available fault current is ~90KAIC. Is that too high to go with MCCB?

kAIC is an interpution rating, you sure you have 90kA of available fault current? That does not sound right for what you have told us about the system so far. Has a short circuit study been done or are you just guessing?

 

[malachi constant]

kAIC is an interpution rating, you sure you have 90kA of available fault current? That does not sound right for what you have told us about the system so far. Has a short circuit study been done or are you just guessing?

Utility company (Xcel Energy) publishes a standard for installation and use. In it is a table of available short circuit current based on transformer size, secondary voltage, overhead or pad-mount, etc. They will not, at least in my experience, provide specific information for a project. They won't even tell you what transformer size they are going to use. In this instance we are somewhere between a 300 and 500 kVA at 208V.

Their table says 300KVA @ 1.4%Z -> 58900 amps, and 500KVA @ 1.4%Z -> 98200 amps. I'm feeding the switchboard with 5 sets of #600 AL, approx 50' run. Using SKM I'm calculating 79kA of fault at the switchboard.

 

[kingpb]

Four choices:

1. Air core reactor
2. ABB makes a device called an Is limiter
3. Make cable run from Transformer to MSD as small of conductor as you can, and make it longer, i.e. adds impedance
4. Use breaker such as Eaton-CH Magnum DS (Good for 85kA)

 

[Jraef]

In addition to those options:

Consult with suppliers about being able to use "Series Rated" gear, i.e. the main in current limiting, so the feeders and sub-panels can have lower kAIC ratings. Sometimes that means the Main will end up being an ICCB in a switchboard that then uses MCCBs for feeders. Some manufacturers have CL MCCBs capable of 100kAIC.

But I emphasize, this is not a "back of a napkin" engineering situation. Budget be damned, this is something that deserves proper attention by a qualified individual. That's a lot of current to be playing guessing games with...

 

[malachi constant]

Wouldn't a BPS solve the rating issue? If I'm not mistaken a 100kAIC rating is a standard option for a BPS. If so, aside from the bad rep that I'm learning BPSs have, this would work, would it not?

 

[Cold Fusion]

Wouldn't a BPS solve the rating issue? If I'm not mistaken a 100kAIC rating is a standard option for a BPS. ...

Yes, it solves that specific issue, but as others have discussed, how are you solving the downstream high fault currents.

Again as the others have discussed, the design solution is integrated. The 90KA does not go away on the loadside of the first OCPD. It lasts until the impedance knocks it down.

cf

 

[malachi constant]

Yes, it solves that specific issue, but as others have discussed, how are you solving the downstream high fault currents.

Again as the others have discussed, the design solution is integrated. The 90KA does not go away on the loadside of the first OCPD. It lasts until the impedance knocks it down.

cf

I give the downstream panels and gear a rating as required to exceed whatever calculated fault current there could be.

Should I assume from the way this conversation has gone that what I've been doing works & meets code, but could be improved upon from a maintenance/safety standpoint? I'm betting I should get a switchgear rep into the office to offer up some pointers.

 

[Jraef]

Wouldn't a BPS solve the rating issue? If I'm not mistaken a 100kAIC rating is a standard option for a BPS. If so, aside from the bad rep that I'm learning BPSs have, this would work, would it not?

Just to be clear, the BPS will have NO "kAIC rating", it is not a fault interruption device, it is a manual switch. The FUSES behind it are what will interrupt the fault, and 100kAIC is fairly common for fuses. The SWITCH itself must have a withstand rating sufficient to be used with fuses at that rating, so in that regard they are OK to use. but still, single phasing is always an issue with fusing.

I know, I'm being pedantic...

 

[Cold Fusion]

... there is nothing wrong with designing to meet, but not exceed, spec. ...

I give the downstream panels and gear a rating as required to exceed whatever calculated fault current there could be. ...

quote=malachi constant;1198675]... Should I assume from the way this conversation has gone that what I've been doing works & meets code, but could be improved upon from a maintenance/safety standpoint? ...[/quote]

I think you are fine.

Once the design meets code and spec, the tradeoff's between maintenance, safety, and lifecycle cost are accounting issues. The owner/owner's agent will tell you.

The only thing a switchgear rep will tell you is to spend money on her equipment.

cf

 

[zog]

Utility company (Xcel Energy) publishes a standard for installation and use. In it is a table of available short circuit current based on transformer size, secondary voltage, overhead or pad-mount, etc. They will not, at least in my experience, provide specific information for a project. They won't even tell you what transformer size they are going to use. In this instance we are somewhere between a 300 and 500 kVA at 208V.

Their table says 300KVA @ 1.4%Z -> 58900 amps, and 500KVA @ 1.4%Z -> 98200 amps. I'm feeding the switchboard with 5 sets of #600 AL, approx 50' run. Using SKM I'm calculating 79kA of fault at the switchboard.

Ouch, that is a tough situation you are in. How are you supposed to make these decisions without even knowing the transformer size? keep in mind that assuming on the high end of your fault current can be a major safety issue too, the higher fault current assumption will likely result ina faster clearing time in the arc flash study, which may cause the calculated Ei to be less than it really is, resulting in workers wearing less PPE than they need to to not be injured.

You need the real data, I have nto dealt with Excel but I have with many other utilities and it is usually just a matter of contacting the right person. Many have an engineer assigned to provising this data to engineering firms doing arc flash studies.