MCA and wiring

[anbm]

Chiller nameplate calls for 2000A MOCP, we showed (5) sets of (3#600kCM, 1#250kCM Ground and 4"C) on our design to feed this chiller.

However, contractor said nameplate indicates MCA = 1,201 Amp. They propose to go with (4) sets of (3#350kCM, 1#250kCM Ground and 3"C) to save some cost and due to constraint space, it makes difficult for 4" conduits run.

It sounds okay to me since we still meet wiring size based on MCA, does anyone has any opinions or see anything wrong with this? Should we bump the wire size to #400kCM instead of #350kCM that contractor proposed...just want to go with a little larger size.

 

[infinity]

The conductors are sized according to the MCA or minimum circuit ampacity. You can have 1201 amp conductors protected at 2000 amps since the 2000 amp OCPD will only be providing ground fault and short circuit protection.

The 4 sets of 350's are fine unless VD is an issue. The 250's as an EGC in each raceway is OK too.

 

[augie47]

barring voltage drop or ambient issues, sounds like a good time to tell your E/C "thanks, great idea"

 

[anbm]

4/0 EGC is not okay with 2,000A CB based on 250-122 table. What is the issue with VFD, Rob?

 

[infinity]

4/0 EGC is not okay with 2,000A CB based on 250-122 table. What is the issue with VFD, Rob?

Oppps, you're correct. (I fixed it). I forgot about the 2000 amp OCPD.

VD or voltage drop. Depending on the length of the run you may want to use larger conductors. Basically it's a design, not a code issue.

 

[anbm]

Got you, I thought you said VFD (variable frequency drive), the chiller and our panel is only 20' away, no voltage drop issue.

 

[jcole]

I would make sure your inspector is ok with it. Some inspectors know the intent of the code on hvac equipment some do not and refuse to discuss.

 

[LarryFine]

I would make sure your inspector is ok with it. Some inspectors know the intent of the code on hvac equipment some do not and refuse to discuss.

That requires an adjustment to the inspection, not the installation.

 

[infinity]

That requires an adjustment to the inspection, not the installation.

______________

 

[Smart $]

The conductors are sized according to the MCA or minimum circuit ampacity. You can have 1201 amp conductors protected at 2000 amps since the 2000 amp OCPD will only be providing ground fault and short circuit protection.

The 4 sets of 350's are fine unless VD is an issue. The 250's as an EGC in each raceway is OK too.

I'm not so sure about this... the 2000A OCPD being okay. If there is an MCA rating on the nameplate, there should also be MF/MCBA rating (max fuse, max cb)...

 

[jumper]

I'm not so sure about this... the 2000A OCPD being okay. If there is an MCA rating on the nameplate, there should also be MF/MCBA rating (max fuse, max cb)...

From OP.......

Chiller nameplate calls for 2000A MOCP

 

[infinity]

The conductors are sized according to the MCA or minimum circuit ampacity. You can have 1201 amp conductors protected at 2000 amps since the 2000 amp OCPD will only be providing ground fault and short circuit protection.

The 4 sets of 350's are fine unless VD is an issue. The 250's as an EGC in each raceway is OK too.

I'm not so sure about this... the 2000A OCPD being okay. If there is an MCA rating on the nameplate, there should also be MF/MCBA rating (max fuse, max cb)...

From the OP:

However, contractor said nameplate indicates MCA = 1,201 Amp

 

[Smart $]

From the OP:

However, contractor said nameplate indicates MCA = 1,201 Amp

Yes... no problem with that.

BUT... there should also be a maximum circuit OCPD rating. That is, if the manufacturer did the calculation to determine MCA, then they also [should have] calculated or otherwise determined the maximum overcurrent condition.

Anyway, before we continue this little debate, we first need to know if this chiller falls under Article 440. If it does, the code progression goes 440.4 where (B) sends one to 440 Part III for determination of SC/GFP device rating. Part III gives a couple options depending on the variables. Not going to get into those right now until we find out the specifics, but it isn't too awful hard to read. There are only two sections to Part III

 

[iwire]

Yes... no problem with that.

BUT... there should also be a maximum circuit OCPD rating. That is, if the manufacturer did the calculation to determine MCA, then they also [should have] calculated or otherwise determined the maximum overcurrent condition.

OK, I am lost.


From the OP.

Chiller nameplate calls for 2000A MOCP,

What more do we need to know?

 

[Smart $]

OK, I am lost.


From the OP.



What more do we need to know?

Well... nothing, I suppose

I recall that being stated in the OP now that you mention it. But on return visits to the thread I forgot about it (didn't reread OP every visit) and was posting under the premise the design criteria did not match the equipment-on-site nameplate data.

 

[iwire]

I recall that being stated in the OP now that you mention it. But on return visits to the thread I forgot about it (didn't reread OP every visit)

Now I am not lost and have been guilty of similar offenses.:grin:

BTW, cool new avatar.

 

[Smart $]

Now BTW, cool new avatar.

Thanks... especially coming from you