LS vs LSI vs LSIG

[JJME]

Hi all,

I wish to know more about when should I put LS, LSI or LSIG breakers in my designs. I've seen some guys do it with a rule of thumb, i.e: if it's an 800A breaker, then it's LS, if it's 1200A, then it's LSI and so on, but I don't want to do it that way.

Do softwares such as ETAP or SKM give you this information? Or is it more like rules in the NEC? I've searched a bit in the Code, but found nothing in it on the matter.

Thanks!

 

[jim dungar]

Generally, I would only specify LSIG.

If you don't need the protective feature it can be turned off. But beware that most Monica itch gear breaker have a self protection Instantaneous protection point at roughly 40kA, but I have never found this to be a coordination issue, as I have not wanted faults of this magnitude to last several seconds.

I am Also an advocate for multiple levels of GF protection, as I preferred limited outage areas rather than the entire building going dark.

 

[petersonra]

Hi all,

I wish to know more about when should I put LS, LSI or LSIG breakers in my designs. I've seen some guys do it with a rule of thumb, i.e: if it's an 800A breaker, then it's LS, if it's 1200A, then it's LSI and so on, but I don't want to do it that way.

Do softwares such as ETAP or SKM give you this information? Or is it more like rules in the NEC? I've searched a bit in the Code, but found nothing in it on the matter.

Thanks!

I think it is all a design decision. Personally, for the difference in price, I agree with Jim on LSIG for higher rated breakers. A lot of times stuff like this needs to be ordered well before you can determine what you really want or need, but it still has to be ordered. I can't recall when I last needed GF on a breaker so don't generally get that, and if TM is adequate that is what I get. But most of the breakers I get are for branch circuits and less than 800 A.

 

[steve66]

The code requires ground fault for breakers over a certain rating.

If selective coordination is required, I will spec whatever is required to achieve the necessary coordination.

If large motor loads are involved, of course you want to make sure the breaker won't trip on starting currents.

And then there is Arc Flash.

So several variables.

 

[petersonra]

The code requires ground fault for breakers over a certain rating.

I think the code requires the circuit have GF protection if the OCPD is over a certain size. The breaker does not have to have it. It could be provided separately or by an upstream device. I think this only applies to services or systems anyway, and not to feeders or branch circuits.

 

[jim dungar]

I think the code requires the circuit have GF protection if the OCPD is over a certain size. The breaker does not have to have it. It could be provided separately or by an upstream device. I think this only applies to services or systems anyway, and not to feeders or branch circuits.

There are similar requirements for feeders as there are for services.

My point was that having layers of GF is easier to coordinate than having it only on the main. GF are also one of the most common fault types, so why not have protection.

 

[petersonra]

There are similar requirements for feeders as there are for services.

My point was that having layers of GF is easier to coordinate than having it only on the main. GF are also one of the most vommon fault types, so why not have protection.

I have only generally included it if a customer asks or it is a service or system. But I only rarely get to systems that big, and IIRC, have only done two services. But, I might have forgotten some over the years.

But I think I have usually included it on MCCBs of 1000 Amps rating or more. Not like I do that many of them these days.

 

[ron]

Keep in mind that every circuit breaker has a longtime, short time and instantaneous trip characteristic, but adding LSI to the breaker symbol on your oneline implies that you have defined that it means you want adjustable characteristics (ass opposed to fixed values) and that you will provide those settings (or specify for a coordination study to be done by a 3rd party), and someone will set those settings on the breaker and maybe even test that they are applied (secondary or primary injection testing). Ground fault trip (adjustable) as has been mentioned, is a code requirement in some cases depending on the voltage and breaker size along with energy reduction at 1200A and above.

 

[Jraef]

Keep in mind that every circuit breaker has a longtime, short time and instantaneous trip characteristic, but adding LSI to the breaker symbol on your oneline implies that you have defined that it means you want adjustable characteristics (ass opposed to fixed values) and that you will provide those settings (or specify for a coordination study to be done by a 3rd party), and someone will set those settings on the breaker and maybe even test that they are applied (secondary or primary injection testing). Ground fault trip (adjustable) as has been mentioned, is a code requirement in some cases depending on the voltage and breaker size along with energy reduction at 1200A and above.

Regular Thermal Mag breakers don’t really have a separate “short time” trip range, the “long time” is roughly equivalent to the I2t trip curve, Instantaneous is the mag trip.