UL1558 and 891

[anbm]

Does anyone know specific difference/advantages between UL1558 and UL891?
Thanks!

 

[ed downey]

Basically the big difference from my point of view is that UL 891 is switchboard construction (Fixed group mounting) & UL 1558 is Switchgear Construction (Individually compartmentailzed draw-out type breakers).

Now there is a mix of draw-out type construction that is not 100% compartmentalized which is a UL 891 compliant.

Depending upon what type of equipment and building type you are looking at will help you determine which type of construction you go with.

Also UL 1558 is much more expensive and usually requires rear access which can take up more space in an electrical room. UL 891 can usually be accessed completely from the front and therefore can be mounted up against a wall reducing the space needed in an electrical room.

-Ed

 

[ron]

1558 switchgear .... has a 30 cycle short circuit withstand rating. This permits you to remove the instantaneous protection component of the main breaker, offering better overcurrent selectivity.

 

[anbm]

One of our project deals with paralleling gear and sale rep. has offered UL1558gear, one of the reasons is they said to do coordination study on emergency side for emergency system.

We can't do this with UL891 gear?

 

[anbm]

1558 switchgear .... has a 30 cycle short circuit withstand rating. This permits you to remove the instantaneous protection component of the main breaker, offering better overcurrent selectivity.

Will you explain more in details what you wrote above?

 

[ron]

Selective coordination is made easier to achieve if you eliminate the instantaneous part of the TCC curve. This can be done because switchgear has been tested to withstand its fault current for a longer period of time (30 cycle) as compared to switchboard construction (3 cycle).
If there is not much redundancy in the quantity of gens, you might want to leave the instantaneous on for the generator breakers anyway to protect the generators from feeding into a fault for long periods of time and damaging the windings.
SWBD construction requires the instantaneous to be on all the time.
Search the internet for selective coordination.

 

[anbm]

Selective coordination is made easier to achieve if you eliminate the instantaneous part of the TCC curve. This can be done because switchgear has been tested to withstand its fault current for a longer period of time (30 cycle) as compared to switchboard construction (3 cycle).
If there is not much redundancy in the quantity of gens, you might want to leave the instantaneous on for the generator breakers anyway to protect the generators from feeding into a fault for long periods of time and damaging the windings.
SWBD construction requires the instantaneous to be on all the time.
Search the internet for selective coordination.

I knew the coordination study, the term 3 and 30 cycles are new to me, did you quoted them from some sources? Thanks!

 

[jim dungar]

SWBD construction requires the instantaneous to be on all the time.

Not absolutely true. Power style UL489 breakers (UL891 ones similar to those used in UL1558 gear) can have their INST function disabled because they are equipped with a 'self-protection' override feature. I regularly selectively coordinate these types of breakers. A common problem, i see, with paralleled generators is that any individual generator protective device is often similar in size to any feeder breaker.

 

[anbm]

Are there any code require to go with UL1558 for coordination study on emergency side? If we can do the coordination study with UL891 gear, I better stick with is since it will be a lot cheaper. On my opinion, UL1558 gear will be a good choice for protection and mantenance purposes.