how to size peak Surge Current Rating per Phase (kA) for SPD

Status
Not open for further replies.
Necnerd

Necnerd

Senior Member
Location
colorado
Occupation
ME
Just hoping to get some understanding on how to size the peak Surge Current Rating per Phase (kA) for an spd. If my understanding is correct It looks like i need to take the sum of the line to neutral current and the line to ground current? is this info something i could from the power company?
 
The surge current rating is not really something you can calculate. It is just how much current the SPD can absorb before becoming damaged. From the few things I have seen about this subject, a 10 kA rating is generally adequate for most situations, as the building wiring tends to limit the current when a surge occurs.
 
This is for a 400a 480v 3 phase service for a wry plant I got quotes a 240ka but wasn’t sure if that was overkill or how to even compare it
 
ctaylo360860 said:
This is for a 400a 480v 3 phase service for a wry plant I got quotes a 240ka but wasn’t sure if that was overkill or how to even compare it
Click to expand...
I am not sure it makes much difference. I am not even real sure that a SPD makes much difference. Anecdotal evidence aside, there just is not much in the way of actual scientific proof that these things actually do as much good as the manufacturers claim.
 
It depends on the system voltage and how close the protector is to the aerial part of the circuit. Here's a fun web bibliography from the M@ster Sp3c supporting docs...

Website Articles
ASCO White Paper, Reasons to Consider Surge Protection Enhancements:
www.ascopower.com/globalassets/documents/asco-white-papers/reasons-to-consider-surgeprotectionenhancements.
pdf?utm_source=newsletter&utm_medium=email&utm_campaign=WP-News-
2018
EC&M: RANKING Electrical Disturbances: www.ecmweb.com/april-2018#12 (First of a seven-part
article)
Electrical Engineering Portal: http://electrical-engineering-portal.com/protection-relay-ansistandards
Health Care Business: www.dotmed.com/news/story/9818
IEEE Standards Association, IEEE Standards Errata and Correction Sheets:
NEMA Electro Industry: www.nemasurge.org/wp-content/uploads/2011/09/Surge-Protective-
Devices—Key-Components-in-Building-Electrical-Infrastructure.pdf
 
JoeStillman said:
It depends on the system voltage and how close the protector is to the aerial part of the circuit. Here's a fun web bibliography from the M@ster Sp3c supporting docs...

Website Articles
ASCO White Paper, Reasons to Consider Surge Protection Enhancements:
www.ascopower.com/globalassets/documents/asco-white-papers/reasons-to-consider-surgeprotectionenhancements.
pdf?utm_source=newsletter&utm_medium=email&utm_campaign=WP-News-
2018
EC&M: RANKING Electrical Disturbances: www.ecmweb.com/april-2018#12 (First of a seven-part
article)
Electrical Engineering Portal: http://electrical-engineering-portal.com/protection-relay-ansistandards
Health Care Business: www.dotmed.com/news/story/9818
IEEE Standards Association, IEEE Standards Errata and Correction Sheets:
NEMA Electro Industry: www.nemasurge.org/wp-content/uploads/2011/09/Surge-Protective-
Devices—Key-Components-in-Building-Electrical-Infrastructure.pdf
Click to expand...
https://www.plantengineering.com/articles/how-to-properly-size-surge-protective-devices/
I had trouble finding some of those articles in the links provided, but this is the article I came across and read.
 
petersonra said:
Basically they just made up these recommendations out of thin air.
Click to expand...
Why is it you say that? Do you think it’s to just sell more product? This is e background of the author.
well, the automation company is asking for spd on service, and 120 branch circuits… do you think this is a good spd, or way overkill?
 

Attachments

  • 7BDDAD68-7E4E-49D6-A0D8-FE835205E7FA.png
    7BDDAD68-7E4E-49D6-A0D8-FE835205E7FA.png
    435.3 KB · Views: 1
I don't think there's anything inherently wrong with having a surge protection device. But I also think they just made up the readings that they think you should have. If you read the article there's no rationale given for the ratings they've chosen other than 123.
 
Gotcha, well I think if I have done anything it will be have over sized the spd and that can’t hurt anything. I got approval for the quote from customer. I was just trying to gain more knowledge on subject or see if what I was reading actually had any truth. Thanks again for always answering my questions
 
ctaylo360860 said:
Gotcha, well I think if I have done anything it will be have over sized the spd and that can’t hurt anything. I got approval for the quote from customer. I was just trying to gain more knowledge on subject or see if what I was reading actually had any truth. Thanks again for always answering my questions
Click to expand...
One other thing! SPDs tend to be leaky in time. The higher current rating you want, the more MOVs are inside the SPD--> more chances of a part leaking. MOVs tend to allow current to pass at normal line voltages. It is not a one-time solution and you have to provide ways to check your SPDs at defined times/ year. Also, lightning strikes can render some of your MOVs to go bust and the next strike, your SPD might not protect your equipment. Been there, got our expensive repeater toast when SPD didn't work as it should.
 
petersonra said:
there just is not much in the way of actual scientific proof that these things actually do as much good as the manufacturers claim.
Click to expand...
I would think they function as advertised. In my mind the question is: how often do these surges happen and at when energy level? Are you aware of any studies on this where statistics have been provided? I am not. Just based on what I have seen being in the field for 22 years, they are extremely rare.
 
electrofelon said:
I would think they function as advertised. In my mind the question is: how often do these surges happen and at when energy level? Are you aware of any studies on this where statistics have been provided? I am not. Just based on what I have seen being in the field for 22 years, they are extremely rare.
Click to expand...
I agree they probably work as advertised. Whether they do much good is something else.
 
Status
Not open for further replies.
Top