What would U Do?

[zog]

I did not-- there are 2 -3 phase geotherm units. One with a mca of 28 amps and the other 18 amps. The fault current to the MLO is about 8k. The big unit is about 75' from the panel with #10 wire while the other is about 50' with #12.

Would this change the results significantly? Or should I use a 25k breaker for those 2 units? I obviously don't know what I am doing and I am about ready to call the dang engineers and tell them what I think. I really don't think this is my job to do and I totally feel out of place here. I can handle all aspects of this job but this.

It is not your job, the engineers should provide you with the fault current data.

 

[RETRAINDAILY]

I believe they may have quoted a series breaker. It was a QGA32200. I read the article posted above on series rating but my brain did not grasp it. What advantage does this give me?

Thanks. I probably am the only one bidding this that is concerned. I bet all others use a 10K breaker at the main distribution panel and no one will ever know-- cept me , of course... If I don't get this job they better do it right cause I'll be watching. :grin:

The way I understand it
With the right main feeding your panel you can coordinate a 10k breaker too. like a LA-frame or J-frame.

your Q-frame is not series rated that would be fully rated. more$$

 

[hardworkingstiff]

I definitely will bid new just curious if anyone has used a refurbished one and should I offer it as an alternative. I get the feeling of "NO" on this one.:grin:

Count me in the no camp.

Have you contacted the SQ D local rep? They will put together a series rated package for you. You may find that you can use 10K breakers in the last panel.

 

[Dennis Alwon]

Count me in the no camp.

Have you contacted the SQ D local rep? They will put together a series rated package for you. You may find that you can use 10K breakers in the last panel.

I believe I can use the 10K in the MLO panel. It's the 1200 amp panel that needs the 65K. At least that's the way I see it based on the calculations.

 

[jim dungar]

your Q-frame is not series rated that would be fully rated. more$$

It is possible to have a series rating with a Q frame breaker, just not the QB's.

 

[Dennis Alwon]

It is possible to have a series rating with a Q frame breaker, just not the QB's.

But mine is a QG and in the table of the link provided it says series rated. ????

 

[jim dungar]

But mine is a QG and in the table of the link provided it says series rated. ????

Yes it is series rated.

 

[Dennis Alwon]

Yes it is series rated.

Thanks Jim.

I guess it is a bit over due with this code change for 2011. I hope you can read it. Basically it is require the available fault current to be marked on equipment with OCPD in other than dwelling units.

 

[zog]

Thanks Jim.

I guess it is a bit over due with this code change for 2011. I hope you can read it. Basically it is require the available fault current to be marked on equipment with OCPD in other than dwelling units.

That is a great idea, is that an approved change to come in 2011?

 

[iwire]

That is a great idea, is that an approved change to come in 2011?

Is it a great idea when the available fault current can change at anytime? (I am not being a wise guy, I am serious)

I see it as a meaningless requirement.

 

[Dennis Alwon]

Is it a great idea when the available fault current can change at anytime?

I see it as a meaningless requirement.

That's why the date etc is required. It would certainly be good in the developing stages, like the job I have where no retail shops have opened in this brand new building. Anyway, I think it is a done deal.

 

[iwire]

That's why the date etc is required.

The data could 'expire' tomorrow or 30 years from now.

As I understand it every time you add / subtract / change transformers, motors etc it can effect the fault current.

Also as I have read here, listing the fault current higher than it really is can be dangerous as that can result in using less PPE than required. Lower fault current can at times (as I understand it) raise the incident energy.

 

[Dennis Alwon]

The data could 'expire' tomorrow or 30 years from now.

As I understand it every time you add / subtract / change transformers, motors etc it can effect the fault current.

Also as I have read here, listing the fault current higher than it really is can be dangerous as that can result in using less PPE than required. Lower fault current can at times (as I understand it) raise the incident energy.

I wish I understood it better to discuss this with you. I would only hope that the transformer would be changed to a similar unit.

If the fault current at the secondaries change every time you add something then the whole concept makes no sense at all. I see the trany with a fault current that remains constant then the wiring gear, etc to the service panel needs another calculation and then from there to the final panel would be yet another right to the end.

If some other retail shop opens up I hope it doesn't change the fault current at the shop I work in otherwise this is worthless. No?

 

[skeshesh]

I have to agree with bob, but Dennis I dont think you need to worry too much about future changes since we're talking about a relatively small system here. The fault current changes that require recalculation are usually at higher voltages and at more sizable facilities with big loads. As suggested by others contact a mfg. and get a series rated quote from them. Finally it does sounds like the engineer didnt deliver due diligence but its not always the engineer's fault. There are some absurdly cheap clients out there that don't want to pay a cent above bare minimums. It is possibly that a short circuit study was not a part of the engineer's design scope.

 

[zog]

Is it a great idea when the available fault current can change at anytime? (I am not being a wise guy, I am serious)

I see it as a meaningless requirement.

Well if it is required to be updated when system modifications are done or a max of every 5 years like the arc flash analysis requirements then it makes sense.

 

[220/221]

The more expensive the part is, the more I make so it doesn't really make sense to assume a greater risk for less money....but I still occaisionally do it.

Refurbished = WD40

We have a local small time guy that has a crapload of old stock.

On high end parts like this I will sometimes give the customer the option, especially in an emergency repair/replace situation.



It has to be the right customer though.

 

[zog]

The more expensive the part is, the more I make so it doesn't really make sense to assume a greater risk for less money....but I still occaisionally do it.

Refurbished = WD40

We have a local small time guy that has a crapload of old stock.

Junk dealers like this are bad for everyone. Here is what "reconditioned" means for a MCCB with thermal trip like the one being discussed. http://www.pearl1.org/standards/Low...1 LV MCCB with Thermal Magnetic Trip Rev5.pdf

A properly reconditioned and tested breaker is "safer" than an untested new one. Unless you test your new one you will be taking a risk.

 

[mxslick]

Is it a great idea when the available fault current can change at anytime? (I am not being a wise guy, I am serious)

I see it as a meaningless requirement.

Me too. A poco transformer or other upgrade in their system would increase the AFC and adding load to an existing network or grid would lower it (or raise it with motor contributions).

Does the Code make provisions for annual (or other timetable) re-calculations to ensure the posted data is still correct?

Stupid idea from our friends at the NEC CMPs. :roll:

 

[zog]

Me too. A poco transformer or other upgrade in their system would increase the AFC and adding load to an existing network or grid would lower it (or raise it with motor contributions).

Does the Code make provisions for annual (or other timetable) re-calculations to ensure the posted data is still correct?

Stupid idea from our friends at the NEC CMPs. :roll:

I have to disagree here. besides a major system change the fault current will not change by much, and having something close is better than nothing at all. I see the aftermath of guesses at AIC applications all the time. Something that is close is better than most peoples guess any day.

 

[jim dungar]

The new code article is for equipment selection purposes, as written it is not intended to be used for arc flash calculations. In fact, it appears there is no reason it even needs to be anywhere near the actual available amount, as long as it is not less than.

It appears the intent is for the purposes that generated the OP. If the equipment was clearly marked 57KA available, then every electrician should be able to determine which breaker rating must be supplied.