Roof top MCC

[m sleem]

In a very sunny weather up to 50 c temp, is it good to have a roof top MCC serves roof top AHUs ? or, better to have a closet in roof top dedicated for MCC where we can provide an AC ?

 

[m sleem]

MCC includes VSD and motor starters

 

[petersonra]

You can put an MCC inside an enclosure or room located on the roof that can be air conditioned.

There are lots of options. I am personally a fan of getting the drives as close to the motors served as practical. It simplifies troubleshooting and installation.

 

[m sleem]

You can put an MCC inside an enclosure or room located on the roof that can be air conditioned.

There are lots of options. I am personally a fan of getting the drives as close to the motors served as practical. It simplifies troubleshooting and installation.

So, it's good idea to have outdoor type MCC beside the equipments despite of excessive heat !

 

[Russs57]

The drives will last much longer at a lower temperature. Plus it will make for a more pleasant and safer working environment.

 

[Coppersmith]

So, it's good idea to have outdoor type MCC beside the equipments despite of excessive heat !

He did say the room can be air condiutioned. (And should be.)

 

[Jraef]

MCCs and VFDs are ALL designed around a maximum 40C (104F) ambient temperature. In some cases there are VFDs that can be de-rated for higher ambient, but that is never the case with an MCC. 40C is the design limit for MCCs in their UL listing procedure. So even with a 3R enclosure, if you put it outdoors on a rooftop anywhere that the air might get over 40C (which from my experience is ANY rooftop), you must add an A/C unit to it anyway, so if you can put in indoors, that's better all around.

 

[Russs57]

IIRC the rule of thumb was you doubled the life of an aluminum electrolytic cap for ever 10 degrees C decrease in temperature.

Used to be you had rack out cap banks that made it possible to change them. Ditto on bolt on diodes. I don't know at what size those things are standard anymore but apparently at sizes larger than I use. So to me anything you can do to increase the life of a VFD is worth looking into......because it seems the days of being able to fix/maintain them is going by the roadside. Or maybe I'd the odd bird who actually replaced caps ever X number of years?

 

[petersonra]

MCCs and VFDs are ALL designed around a maximum 40C (104F) ambient temperature. In some cases there are VFDs that can be de-rated for higher ambient, but that is never the case with an MCC. 40C is the design limit for MCCs in their UL listing procedure. So even with a 3R enclosure, if you put it outdoors on a rooftop anywhere that the air might get over 40C (which from my experience is ANY rooftop), you must add an A/C unit to it anyway, so if you can put in indoors, that's better all around.

I've been in a fair number of penthouses that are over 40 degrees C now and then. Many are not air conditioned.

 

[Jraef]

I've been in a fair number of penthouses that are over 40 degrees C now and then. Many are not air conditioned.

No argument, me too. Doesn't mean it's kosher though. In fact every time I point that out to a consultant who says that an MCC must be rated for 50C (sometimes more), they are shocked to learn that UL/NEMA specs state 40C max. Back in th days before power electronics migrated into MCCs, people didn't pay much attention because it didn't really affect contactors and such, although it does technically affect breaker tripping curves.