surge protector

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domnic

Senior Member
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Electrical Contractor
I have a customer that's wants to me to put surge protectors on 4 5 ton 208 3 phase AC unites. he has a 400 amp 208 3 phase service. should I put a protector at each AC disconnect or one at the service the full load of the service is 230 amps. what size at service or at each disconnect? the ac units pull 30 amps each.
 
domnic said:
I have a customer that's wants to me to put surge protectors on 4 5 ton 208 3 phase AC unites. he has a 400 amp 208 3 phase service. should I put a protector at each AC disconnect or one at the service the full load of the service is 230 amps. what size at service or at each disconnect? the ac units pull 30 amps each.
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Depends on what he has and what he wants and what he's willing to spend.

Are these RTU's in an area subject to lightning? Or are you more concerned with POCO surges?

For a comprehensive overview of surge suppression you can visit www.nemasurge.org (thanks to whoever it was on here that turned us on to that)
 
domnic said:
I have a customer that's wants to me to put surge protectors on 4 5 ton 208 3 phase AC unites. he has a 400 amp 208 3 phase service. should I put a protector at each AC disconnect or one at the service the full load of the service is 230 amps. what size at service or at each disconnect? the ac units pull 30 amps each.
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the load is immaterial.

personally, i would be inclined to put a type 1 SPD right at the service (or at least as close as I could get to it), and a type 2 SPD out at each A/C unit. I think I would not put it at the disconnect unless there is no place closer to the unit where I could put it.

having said that, I would also want to know why it is that he has out of the blue decided this is a good idea.
 
petersonra said:
the load is immaterial.

personally, i would be inclined to put a type 1 SPD right at the service (or at least as close as I could get to it), and a type 2 SPD out at each A/C unit. I think I would not put it at the disconnect unless there is no place closer to the unit where I could put it.

having said that, I would also want to know why it is that he has out of the blue decided this is a good idea.
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I have been taught that once you put the type 1 SPD on the main, it is a total waste of money to put any kind of surge protection down the line. But I could have been taught wrong. Also if your client wants protection from lightning, as far as I know there are no SPD that will stop that. Lightning is one bad a**. You would want a lightning protection system for that.
 
Some of the induced voltage effects of a nearby lightning discharge can be developed in the house branch and feeder wiring itself. A Type 1 at the main will not provide the best possible protection against that.
The ideal place to protect against that type of induced voltage is as close as possible to the equipment being protected.
 
SPD Effectiveness

SPD Effectiveness

GoldDigger said:
Some of the induced voltage effects of a nearby lightning discharge can be developed in the house branch and feeder wiring itself. A Type 1 at the main will not provide the best possible protection against that.
The ideal place to protect against that type of induced voltage is as close as possible to the equipment being protected.
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I agree.
See attached email discussion, read from bottom up.
 

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Haji said:
If it is microprocessor controlled with no inbuilt surge protection, it is a good idea.
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petersonra said:
why would that be?
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Motors in the HVAC unit can take a pretty good surge and not cause any trouble, electronics in the controls however are much more vulnerable to surges. If anything some protection on the control voltage source is best for the control circuit, but anything upstream is going to at least take some of the punch out of anything that gets through.
 
It depends

It depends

The need for more than one surge protector depends on the configuration and how the lightning is likely to come in. Most of the time, one on the main is sufficient. How big depends on where you live and the history of the area. 110KA is often a good size.

We have a building now where there is a long run of conductors to an isolated panel near a spot where they have had multiple hits in the past. The lightning could easily come in over building steel and get into the electrical circuits. Therefore we will add a surge suppressor there.
 
Not Just Lightning Strikes

Not Just Lightning Strikes

dema said:
The need for more than one surge protector depends on the configuration and how the lightning is likely to come in. Most of the time, one on the main is sufficient. How big depends on where you live and the history of the area. 110KA is often a good size.

We have a building now where there is a long run of conductors to an isolated panel near a spot where they have had multiple hits in the past. The lightning could easily come in over building steel and get into the electrical circuits. Therefore we will add a surge suppressor there.
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Dema, you need to open up your mind and do some research.
Customer loads are vulnerable to more than just lightning strikes.
That is why electrical standards are written and developed.
PFCC failures, drunks hitting power poles, construction accidents, etc can wreck havoc on plant operations anywhere. I just responded to an incident at SFO airport where a construction crane toppled a 230KV tower on Hwy 101 here that caused multiple failures of solid state equipment throughout the whole airport. My work involved repair of a failed ATS. These types of overvoltage spikes can take their toll on sensitive equipment anywhere, not just in lightning prone areas.
 
ATSman said:
Dema, you need to open up your mind and do some research.
Customer loads are vulnerable to more than just lightning strikes.
That is why electrical standards are written and developed.
PFCC failures, drunks hitting power poles, construction accidents, etc can wreck havoc on plant operations anywhere. I just responded to an incident at SFO airport where a construction crane toppled a 230KV tower on Hwy 101 here that caused multiple failures of solid state equipment throughout the whole airport. My work involved repair of a failed ATS. These types of overvoltage spikes can take their toll on sensitive equipment anywhere, not just in lightning prone areas.
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And I's say that surge equipment was intended more so for those incidents then the lightning incidents. They work good for nearby lightning but if you are seeing direct hits frequently - you are seeing damage frequently.
 
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