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Series ratings of Square D breakers

Series ratings of Square D breakers

Series ratings of Square D breakers

(OP)
I am trying to determine if a Square D type NEHB panelboard with type EHB branch circuit breakers (both discontinued) can be used in series with a type KI breaker, on a system with approx. 35kA available fault current.  

The EHB breakers are rated for 14kA at 277/480, but literature from our Square D binder indicates that when they are applied to the load side on an I-LIMITER breaker, they are UL listed for use on systems with up to 100kA avail. fault current.  

The KI breaker is a current-limiting device, and carries the I-LIMITER name.  However, since the KI series of breakers came out well after the NEHB literature stating the series-rating conditions, I'm hesistant to assume that KI and NEHB are automatically compatible under this fault current condition.

Unfortunately, all of Square D's series-connected compatibility charts only cover their current lines of breakers and panelboards.  So there are no cross-referencing information on EHB breakers (or NEHB boards) with type KI breakers.  

If we get our I-Line panel with a factory-installed KI breaker, the added cost of the breaker will easily offset the labor & materials required to replace the downstream NEHB panel with a modern NF panel (in which case we would only need a type KC breaker in the I-Line), and to re-terminate all of the existing branch circuits on the new panel.  

If the existing NEHB panel was quite old, I would replace it without hesitation.  But it's a 1996 vintage, a little too new to demo if I can justify otherwise.  

RE: Series ratings of Square D breakers

Only SQ-D can answer your question.

Series rating is strictly determined by UL testing, (may also be ETL)  and not by design.

A particular pair must have been tested and certified by UL to have a sereies rating.

You may want to explore possibility of inserting fuses in the circuit somewhere (say main device)as most breakers are series rated with most type of fuses. You still need to verify the rating with mfr.

RE: Series ratings of Square D breakers

A new section in the 2005 NEC specifically permits series combinations to be selected "under engineering supervision" for existing installations. The combination must be approved by a licensed engineer, but it seems to permit the combination to be applied without testing or UL approval.

RE: Series ratings of Square D breakers

According to Square D Digest 169 (1992), At 480Y/177V, there is(was) a 65kA series rating for a 225A max type KI with 15-60A EH/EHB breakers.

Hope that helps.

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