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 Post subject: Main PD isolation
PostPosted: Tue Sep 22, 2020 6:12 am 

Joined: Fri Sep 18, 2020 1:31 am
Posts: 1
Hi,

What are the criterias for considering a SWBD incomer as arc isolated? I can not see that the IEEE 1584 standard says any specific about this. May this be referred to the SWBD design form factor, e.g. 3b or 4b, or must the SWBD design be arc tested (perhaps both?), or are there some other criterias / standards to consider?

What about installing a arc guard system, or applying an ERMS (e.g. schneider MasterPact MTZ ERMS) for a SWBD where there is a maximum incident energy design requirement. Is this sufficient, or must the arc guard send a trip signal to the upstream breaker of the incomer?
Must the ERMS be applied in the upstream breaker of the incomer, or must the incomer breaker be sufficient arc isolated if ERMS are applied in this?

Is this a matter of conducting a risk assessment, or are there any clear guidelines for this?

I hope the question(s) was clear, and that you will share you views on this.

Best regards,
Lars.


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 Post subject: Re: Main PD isolation
PostPosted: Mon Sep 28, 2020 8:53 am 

Joined: Mon Aug 20, 2018 6:03 am
Posts: 9
To my knowledge there is no clear guidance on this issue. When is an internal barrier enough to separate a volume into 2 arc flash incident energy zones?

It is a matter of opinion as far as I know unless somebody has done some testing. Evaluating this was not within the IEEE 1584 WG scope. NFPA 70E has not weighed in. In fact, even AR type 2C equipment which is widely believed to barrier one compartment from another is always tested with all the doors closed. So there is no test to prove that if you are in front of a open compartment, its barriers, will protect you from an AF even in a neighboring compartment. Many assume that, but it is an untested hypothesis in most cases.

Need to be careful with safety related claims that have no empirical basis or rigorous analytics behind them. Too easy to have an "opinion" based on personal experience or "common sense" that does not have enough data or analysis to support it.

When adding protection such as an ERMS, or changing trip units or relays, etc. The more upstream it is the broader the zone it protects. As long as the threshold can be set appropriately it should work. Of course that may imply a certain sacrifice in selectivity, but that may be acceptable under the circumstances.


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