ETU Setting Procedure - Low Voltage Main breaker

[Charz]

Hi,

I would like to learn, how to set the ETU settings of a low voltage ICCB breaker which has a ETU (Electronic Trip unit). The outgoing loads are the final loads (Mixed of HVAC motors, fans & compressors). This breaker is an Main breaker in a MCC Panel.

say, I have a bus bar rating of 800A & the Incomer breaker rating is of 800AT, the actual demand load is 452Amps.How do I set the LSI breaker settings in this case?

Should I set the "L" rating to 800A or for "452A"?
How about the "S" and "I" settings?

What is the general procedure to set the ETU?

 

[xptpcrewx]

Hi,

I would like to learn, how to set the ETU settings of a low voltage ICCB breaker which has a ETU (Electronic Trip unit). The outgoing loads are the final loads (Mixed of HVAC motors, fans & compressors). This breaker is an Main breaker in a MCC Panel.

say, I have a bus bar rating of 800A & the Incomer breaker rating is of 800AT, the actual demand load is 452Amps.How do I set the LSI breaker settings in this case?

Should I set the "L" rating to 800A or for "452A"?
How about the "S" and "I" settings?

What is the general procedure to set the ETU?

Great question. I started a thread related to LSIG setting requirements titled, “Overcurrent Protection Assumption” and the NEC appears to not have any direct information about LSIG.

LT pick-up I believe would be per Article 430 and not greater than the rating of the bus bars. All other settings would be based on what makes sense coordination-wise.

 

[ron]

Great question. I started a thread related to LSIG setting requirements titled, “Overcurrent Protection Assumption” and the NEC appears to not have any direct information about LSIG.

LT pick-up I believe would be per Article 430 and not greater than the rating of the bus bars. All other settings would be based on what makes sense coordination-wise.

I agree with Xptpcrewx. If the equipment is rated at 800A, the long time pickup is generally then 800A. Everything else depends.

It depends on what it is feeding, whether ground fault is needed, whether it needs to be selective with something upstream or downstream, whether it needs to overcome inrush, etc.

 

[topgone]

Hi,

I would like to learn, how to set the ETU settings of a low voltage ICCB breaker which has a ETU (Electronic Trip unit). The outgoing loads are the final loads (Mixed of HVAC motors, fans & compressors). This breaker is an Main breaker in a MCC Panel.

say, I have a bus bar rating of 800A & the Incomer breaker rating is of 800AT, the actual demand load is 452Amps.How do I set the LSI breaker settings in this case?

Should I set the "L" rating to 800A or for "452A"?
How about the "S" and "I" settings?

What is the general procedure to set the ETU?

L = long time setting, the overload protection of the load.
S = short-time setting, the current you expect of the load during energization/inrush/ starting current and the duration of inrush/starting current.
I = instantaneous setting, the current available when the load gets faulted. You must set this to the highest possible setting if your breaker is the main breaker.
G = ground protection,required by code when your breaker is 1000A or higher. You will only be allowed to skip this requirement if opening such breakers will result into the processes served to be in danger if tripped.

 

[xptpcrewx]

S = short-time setting, the current you expect of the load during energization/inrush/ starting current and the duration of inrush/starting current.

S gets set “above” inrush and starting current.

I = instantaneous setting, the current available when the load gets faulted. You must set this to the highest possible setting if your breaker is the main breaker.

You definitely do not just arbitrarily set this to max just because it’s a main breaker.

 

[Jraef]

The proper procedure is to perform, or have someone perform, a “coordination study” before making final adjustments. A properly coordinated system ensures that a fault is cleared by the protective device closest to the fault. In other words you don’t want to trip the main and shut down everything just because there was a minor fault on a small branch circuit, but the sensitivity of the main was set lower than the branch device.

 

[ATSman]

The proper procedure is to perform, or have someone perform, a “coordination study” before making final adjustments. A properly coordinated system ensures that a fault is cleared by the protective device closest to the fault. In other words you don’t want to trip the main and shut down everything just because there was a minor fault on a small branch circuit, but the sensitivity of the main was set lower than the branch device.

I totally agree. The power systems study and coordination study, usually performed and stamped by a registered PE (E.E.) in that state. It's all about liability and $$ when the s - - t hits the fan and the finger pointing starts. That's why they make the big bucks!

 

[iceworm]

Q: Is this 480V industrial, or 208V commercial. The loads sound like commercial building stuff. Probably doesn't matter much - mostly just curious.

Assumptions:

The system is standard stuff - no iron lungs, no alien containment fields, no COPS.
With this size panel boards, the system is in the area where there was a design and drawings. All the load calcs should be done - panels, xfms, feeders selected.​

Disclaimer: I've been doing this for a lot of fricken years, but I didn't look any of this up and I tend to use common, colloquial terms. There could easily be some terminology errors. Like all free advice, it is worth what you paid for it.

First: Get the mfg TCC sheet. Read all the notes.
Second: I don't care if you have Etap, SKM, or the like (or not), rtfm

As discussed, the settings are all about coordination. If you don't happen to have Etap, or SKW, or the like, you can do this taping the TCC sheets up on the window. Yes, if there is not a lot to do, it will work just fine - probably faster.
Keep in mind:

"coordination" is defined as "daylight between the curves"
All of the TCC curves have a tolerance -the line is thick
It's damn near impossible to coordinate down to zero time
You have to do the smallest CB first then move back up stream.​

LT: This is really the only one the NEC cares about
I'd start with the transformer and feeder conductors going to the panel. Often the panel main is the OCPD for the xfm secondary and the panel feeder conductors. Yes, you want to set the LT as high as you can. If the xfm and conductors are good for it, right up to 800A.

The ST setting will be the most interesting. The major reason to set this as low as possible is to lower the arc-flash. All understand the safety issues, but the real reason is the techs don't want to don a moon suit to take a voltage measurement. If you can get the arc-flash down to where the ppe is gloves, glasses, FRs, and a hardhat - you will be a hero. If the trip unit has a maintenance switch (anything new should), set maintenance mode ST time dial to zero (no intentional delay) - This is as close as you will get to "hero" status.

Pick out the biggest panel board feeder CB. Main CB ST has to be outside of that. (This makes the assumption that the panel board feeder is selected to handle the load inrush.
Survey all the loads and estimate a "global inrush" worst case during power restoration. Mark that on your coordination TCC. Main CB ST has to be outside of that.​

Instantaneous setting:
Depending on how stiff the bus is, and the main CB/feeder ratio, you may never get this to coordinate. For example:

225kva , 208V, 2%Z and infinite bus, ASCC = 31KA
1000KVA, 208V, 5%Z, infinite bus, ASCC = 56KA​

Now is a great time to check if the CB are rated for the SCC. Because if they are not, that is going to be a mess.
Typical molded-case T-M I kicks in 20X - 40X.
Typical LSI is adjustable from 2X - 15X
With an 800A LSI main, and a 400A TM feeder. The I won't coordinate.
With 100A T-M feeders, maybe you can get it to coordinate.

I would recommend a class. The local IEEE chapter likely does these. (edit to add following Jaref's post) Or not. Hopefully there is a local equivalent to IEEE with classes.

the worm

 

[Jraef]

Well as I look more carefully the OP is in Tashkent, a city in Uzbekistan. So it's unlikely that the U.S. NEC applies, and we don't know what their equivalent of a "PE" would be.

But the need for a coordination study is still there.