Fused Disconnect At Rooftop Equipment?

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Fitzdrew516

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Cincinnati, OH
I received a submittal that showed a fused disconnect at an AHU. I had spec'd a non-fused disconnect in this location due to the disconnect being needed for disconnecting means only and not over-current protection. When we questioned the manufacturer they said this:

"for code and service purposes we have a dual disconnect system. One circuit breaker inside the control panel and a fused arc flash disconnect on the outside. We need the fused disconnect to be able to service without the full protective clothing requirement."

Now am I missing something here? It is my understanding (and has been for a long time) that there is no code requirement for OCP at equipment. I'm pretty sure the manufacturer is wrong regarding the code requirement, but regardless if it's in the instructions it would fall under 110.4 (B) anyway. Thoughts?

Thanks,
-Drew
 
I am not sure that a fused disconnect effects the arc flash potential or the minimum PPE required inside the arc flash boundary in any way. It certainly does not get someone out of doing the calculations and coordination as far as I know.
 
Maybe what is really happening is that the equipment inside the enclosure does not meet the required/labelled SCCR without the series rated fused disconnect?
 
GoldDigger said:
Maybe what is really happening is that the equipment inside the enclosure does not meet the required/labelled SCCR without the series rated fused disconnect?
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I suppose that could be possible. I'm gonna stick with my response of although it's not required by the NEC if they tell you that it has to be fused now it's required by the NEC.
110.4 (B) is one of my favorite requirements in the NEC because if I were writing the instructions for equipment I would totally put something in there like "Installer shall eat peanut butter & jelly sandwich while installing equipment (chunky or smooth is acceptable)". Now it's an NEC requirement to eat a PB&J.
 
with fuses you will be asked if it is "likely to be energized" where is thr OCPD for this equipment is it readily accessible at all times?
 
Fitzdrew516 said:
I received a submittal that showed a fused disconnect at an AHU. I had spec'd a non-fused disconnect in this location due to the disconnect being needed for disconnecting means only and not over-current protection. When we questioned the manufacturer they said this:

"for code and service purposes we have a dual disconnect system. One circuit breaker inside the control panel and a fused arc flash disconnect on the outside. We need the fused disconnect to be able to service without the full protective clothing requirement."

Now am I missing something here? It is my understanding (and has been for a long time) that there is no code requirement for OCP at equipment. I'm pretty sure the manufacturer is wrong regarding the code requirement, but regardless if it's in the instructions it would fall under 110.4 (B) anyway. Thoughts?

Thanks,
-Drew
Click to expand...

If the fuse is included in the arc-flash analysis, then it has the potential of reducing the incident energy at the equipment.
If you have more than 10kA available at the air handler, then the fuse is required to allow the disconnect switch to meet the short-circuit requirements of the system. And as someone else mentioned, it may be listed/tested with the breaker in the AHU to meet the system AIC requirement.
 
Fitzdrew516 said:
"Installer shall eat peanut butter & jelly sandwich while installing equipment (chunky or smooth is acceptable)". Now it's an NEC requirement to eat a PB&J.
Click to expand...

You need to specify bread type and style. Is a whole sub roll acceptable or must one use regular sliced white? I am a sourdough baguette guy myself, but I am willing to adapt.
 
Fitzdrew516 said:
I s...C.
110.4 (B) is one of my favorite requirements in the NEC because if I were writing the instructions for equipment I would totally put something in there like "Installer shall eat peanut butter & jelly sandwich while installing equipment (chunky or smooth is acceptable)". Now it's an NEC requirement to eat a PB&J.
Click to expand...

No exception for people with peanut allergies!?!?
 
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