Overcurrent Protection Coordination

[A-1Sparky]

We recently had a 4000 amp main trip from thermal overload of a downstream breaker. This caused the loss of power to three buildings. An overzealous and undereducated maintenance electrician reset the main without determining the cause of the outage. Luckily, just the downstream breaker tripped upon reenergization. I want to minimize outages through selective overcurrent protection coordination of our equipment. We have relatively new (10 years old or so) Square D switchgear with electronically adjustable breakers. I'm quite sure they were just left at the factory default setting. Is this something that I can tackle with the proper manual(s), or should I bite the bullet and hire it out to the ridiculously expensive Square D Tech team?

 

[jim dungar]

We recently had a 4000 amp main trip from thermal overload of a downstream breaker. This caused the loss of power to three buildings. An overzealous and undereducated maintenance electrician reset the main without determining the cause of the outage. Luckily, just the downstream breaker tripped upon reenergization. I want to minimize outages through selective overcurrent protection coordination of our equipment. We have relatively new (10 years old or so) Square D switchgear with electronically adjustable breakers. I'm quite sure they were just left at the factory default setting. Is this something that I can tackle with the proper manual(s), or should I bite the bullet and hire it out to the ridiculously expensive Square D Tech team?

What is the cost of another unexpected outage versus that of hiring somone with the experience in performing a coordination study?

After someone has determined the correct/acceptable settings, how will you know that the breakers will actually "follow" them without testing the breakers?

And no, you do not need to go to the specific breaker manufacturer, there are many companies, that do this for a living not as a side job, to choose from.

 

[Pierre C Belarge]

Adding to Jim's post;
What would it cost you, if you set the values, it trips again and one of the tenants wants you to pay for their loss during this new outage?

Professionals are almost always less cost in the end.

 

[zog]

Jim made some good points, best bet is to farm it out but no reason to use Square D. I can vouch for these guys, they do this everyday and are in your area.

http://www.99aetco.com/

Charlie is the guy you want to talk to about this.

Also with your gear being new there is a good chance you have ZSI already in place to orevent this type of thing, it just needs to be set up right. 10 years old you probally have DS-II breakers with Digitrip trip units right?

 

[weressl]

We recently had a 4000 amp main trip from thermal overload of a downstream breaker. This caused the loss of power to three buildings. An overzealous and undereducated maintenance electrician reset the main without determining the cause of the outage. Luckily, just the downstream breaker tripped upon reenergization. I want to minimize outages through selective overcurrent protection coordination of our equipment. We have relatively new (10 years old or so) Square D switchgear with electronically adjustable breakers. I'm quite sure they were just left at the factory default setting. Is this something that I can tackle with the proper manual(s), or should I bite the bullet and hire it out to the ridiculously expensive Square D Tech team?

I think it is clear that you need a comprehensive short circuit, coordination and arc-flash study performed on the system. Square D is not your only solution. Large firms have tools and resources, but also huge overheads and profits to cover. A smaller engineering firm or even an independent engineer specializing in such studies can offer you servies at a much more reasonable rate. (Perhaps the Engineering firm performing the original design?) Make sure that the study performed by utilizing a commonly used software and that you get all the data files as part of the Contract, for the record and that future expansion can be accomodated and the study revised at an incremental cost.

The adjustment should be performed as part of the study, requirements should note that adjustment and modifications to the system and settings shall be that regular maintenance can be performed utilizing the lowest practical arc-flash exposure - while maintaining operational relaibility - and corresponding PPE requirements.

 

[charlie b]

Selective coordination is not an NEC requirement, except for a few very specific installations that do not include yours. It is a design decision. But it is not a simple one to make. There are other considerations that must be addressed. For example, if you intentionally delay the tripping of an upstream breaker, such as the main breaker on the main service panel, in order to give time for the downstream breaker to trip first, then you add a significant amount of energy to the fault point. That alters the arc flash energy, and thereby alters the level of personal protective equipment needed to work on the equipment.

 

[A-1Sparky]

10 years old you probally have DS-II breakers with Digitrip trip units right?[/QUOTE]

Yes, they are the DS-II breakers with the Digitrip units.

 

[A-1Sparky]

Jim made some good points, best bet is to farm it out but no reason to use Square D. I can vouch for these guys, they do this everyday and are in your area.

http://www.99aetco.com/

Charlie is the guy you want to talk to about this.

Also with your gear being new there is a good chance you have ZSI already in place to orevent this type of thing, it just needs to be set up right. 10 years old you probally have DS-II breakers with Digitrip trip units right?

Thanks for the link, Zog. I'll probably get a hold of Charlie and pick his brain a little.

 

[A-1Sparky]

Selective coordination is not an NEC requirement, except for a few very specific installations that do not include yours. It is a design decision. But it is not a simple one to make. There are other considerations that must be addressed. For example, if you intentionally delay the tripping of an upstream breaker, such as the main breaker on the main service panel, in order to give time for the downstream breaker to trip first, then you add a significant amount of energy to the fault point. That alters the arc flash energy, and thereby alters the level of personal protective equipment needed to work on the equipment.

I always use level 4 PPE with a 40 cal rating in these type of situations. Adjustments to the trip settings wouldn't merit a higher level of PPE than that, would it?

 

[brian john]

Anybody can set the adjustable trips on a CB, but getting to the point where you are ready to pull your tweaker out requires quite a bit.

1. Coordination study by a firm that KNOWS WHAT THEY ARE DOING.
2. Testing of the CBs by a firm that KNOWS WHAT THEY ARE DOING.

 

[ron]

A-1, sometimes the incident energy is > than 40 cal/cm^2, so your suit might not be enough

 

[zog]

10 years old you probally have DS-II breakers with Digitrip trip units right?

Yes, they are the DS-II breakers with the Digitrip units.[/QUOTE]

Well they should have ZSI capability, check to see if it is enabled, look for a small dip switch at the bottom of the Digitrip.

 

[A-1Sparky]

Thank you all for the info. and replies. Looks like I'll be shopping for coordination study/breaker testing quotes. :grin:

 

[Pierre C Belarge]

A-1
Sometimes we think we are inadequate when we have to call someone else to do work we think we are smart enough for. As one becomes more experienced, we realize it is not so bad to pass the responsibility on to others...and learn at the same time.
Good luck with the study.

 

[A-1Sparky]

Thanks, Pierre. I'm sure I could figure it out, it just might take me a year or two. :wink: