Smaller Equipment Replacement

[United36]

Hello,

I am working on a project where we are replacing a number of Rooftop AC units (RTUs). The units are getting smaller (less electrical load etc..). My question is...Do we have to prepare a load/panel schedule for these switch board panels? We are not adding anything to the existing panel, but we will have to change the fuse size (smaller). There are other parts of this project that will require engineered electrical drawings but for these panels how would I treat them on an electrical plan? It seems like I would not need to determine the existing load of the panel if I am downsizing the electrical load.


Any thoughts would be appreciated!

Thanks!

 

[hmspe]

This would vary by jurisdiction. I recommend you ask the building official or the inspector.

 

[infinity]

hmspe gave you some good advice and I would ask first. There's a town near here where if you replace a RTU (even with a with a smaller and lighter replacement) the building official will require you to get a structural framing inspection. I'm not making this up. hmy:

 

[Jraef]

hmspe gave you some good advice and I would ask first. There's a town near here where if you replace a RTU (even with a with a smaller and lighter replacement) the building official will require you to get a structural framing inspection. I'm not making this up. hmy:

Similar thing happened to me. Because of a down-size on a wash plant at a gravel pit, I got a project to replace a 400HP pump that was no longer needed with a 100HP pump on a VFD. The AHJ insisted that I do a new load calculation on the switchboard, even though I did not change the feeder circuit or conductors going to the new VFD (it had it's own circuit breaker inside). Didn't matter, he made me do it anyway. I had done a similar project at the same facility a year earlier but had a different inspector (from the same city), he said no such thing. I had to eat it because I was ASSuming I would not need to perform that task (and delay) on this new project. I thought about arguing with the inspector, but I reminded myself of that old adage about mud wrestling with a pig.

 

[MarineTech]

Very good advice so far.

Which code cycle are you on?

For NEC 2011, I would check if rooftop circular raceways temperature adjustment per Table 310.15(B)(3)(c) correspond to the conductors installed, even if the load is going down.

 

[United36]

Believe it or not the Village is still on NEC 1993. Any thoughts as to how this would impact this issue?

Thank you all for the advice so far... it just seems absurd to do an load calcualtion on an exisiting panel, for equipment replacement, when the load is going down. Is there some logic I am missing here, safety wise or other?

Thanks!

 

[MarineTech]

Believe it or not the Village is still on NEC 1993. Any thoughts as to how this would impact this issue?

Thank you all for the advice so far... it just seems absurd to do an load calcualtion on an exisiting panel, for equipment replacement, when the load is going down. Is there some logic I am missing here, safety wise or other?

Thanks!

NEC 2008 Table 310.15(B)(2)(c) = NEC 2011 Table 310.15(B)(3)(c); Ambient Adjustment for Circular Raceways (Conduit) Exposed to Sunlight on or above Rooftops. I believe this ambient correction adder first appeared in NEC 2008. It is based on experimental data. For me it demonstrates a concept that I have known for some time. That is, Sunlight heating effects on rooftop conduit can be substantial, and needs to be addressed in sizing conductors in conduit on a rooftop. One might also ask, what about conduit on a wall exposed to sunlight? Doesn't this also require an adder for direct sunlight?

 

[GoldDigger]

One might also ask, what about conduit on a wall exposed to sunlight? Doesn't this also require an adder for direct sunlight?

I suspect that part of the difference is that the wall will not get as hot as the roof because of the convective cooling that the vertical surface has and the roof does not.
Going on from there, the ambient air around the conduit above a hot roof will be heated, while the ambient air around a conduit attached to a wall will not.

The heat going into the conduit from the sun is also reduced by the angle of the conduit to the sun, while the roof conduit will often be perpendicular to the sun's rays some of the time.

So,
1. The direct sunlight is less for the wall.
2. The cooling is much better.