Wiring a boiler

[Designer69]

I need to properly wire a boiler with what appears to be 5 zone circulating water pumps.

I believe a Taco type zone controller will be used. The circulating pumps are 1/2 HP, 5 amps.

My questions are:

-Does this look like the proper way to wire this? (Pic. attached)

-Per NEC article 430.110 and the example in the handbook, a 5 HP - 30 Amp, 120V-1P disconnect switch would be required. Does this even exist and isn't it very expensive?

-Per the wiring in the pic, am I even allowed to have a 120V-1P, 30A branch breaker?

 

[ActionDave]

Are you sure your zone pumps are .5 HP?

 

[Designer69]

That's what it says on the mechanical schedule.

Perhaps it's a mistake? It does seem a bit high.

 

[augie47]

I would check further.. 1/2HP @ 115v would be closer to a 10 amp load.
I would be great to have a picture of the motor nameplate to confirm HP, voltage and if they are thermally protected.

 

[ActionDave]

That's what it says on the mechanical schedule.

Perhaps it's a mistake? It does seem a bit high.


View attachment 20435

Your image shows a bell and gosset pump, 1/2 HP would not be unusual for those pumps. Now I need to ask what is the application?

 

[Designer69]

Yes and they say 5 Amp FLA on spec sheet.

The application is a R-2 type occupancy. Dormitory house, 2 stories with basement and attic. 2 dwelling units plus individual sleeping rooms.

This is a Lochinvar WHN 199 boiler.

 

[ActionDave]

Yes and they say 5 Amp FLA on spec sheet.

The application is a R-2 type occupancy. Dormitory house, 2 stories with basement and attic. 2 dwelling units plus individual sleeping rooms.

This is a Lochinvar WHN 199 boiler.

Ok. This is a commercial boiler project and not something you scratch out on a napkin, which is about what you are going to get asking questions on an internet forum. This is a great site for information but I would say you need some direct input from an on site engineer.

 

[Designer69]

Yes you're right. I'm going to call the mfg. on Tuesday and ask how this is typically connected but I wanted to see if I'm on the right track to begin with.

 

[kwired]

I think you got asked if you were sure they were 1/2 hp, because most residential boilers would only have about 1/20 to 1/10 circulator motors, and probably only 3/4 or 1 inch piping.

You appear to have a larger system and probably larger zones 1/2 hp might actually be considered a small pump for those that are around these systems much.

That said for general motor circuit calculations - T 430.238 is where you are supposed to get FLA from - and a 1/2 hp 115 V motor in that table says 9.8 amps.

I don't think 430.53(A) will let you put all of them on one branch circuit - it would have to be 20 amp max OCPD and there is just too many for that.

 

[hbiss]

I believe a Taco type zone controller will be used.

Taco zone controllers have a maximum combined load of 20A. The SR506 can handle 6 zones but you have the 20A limitation. So I would use five single zone controllers (SR501), one for each circulator. Then I would use a single pole switch between each SR501 and the respective circulator as a disconnect. Then provide two 20A circuits, supply three relays from one and the remaining two from the other. Mount this all on a backboard with a trough along the bottom. Relays and disconnect switches coming off the trough with nipples or offset nipples.

-Hal

 

[Designer69]

Taco zone controllers have a maximum combined load of 20A. The SR506 can handle 6 zones but you have the 20A limitation. So I would use five single zone controllers (SR501), one for each circulator. Then I would use a single pole switch between each SR501 and the respective circulator as a disconnect. Then provide two 20A circuits, supply three relays from one and the remaining two from the other. Mount this all on a backboard with a trough along the bottom. Relays and disconnect switches coming off the trough with nipples or offset nipples.

-Hal

Thank you, this sounds good. Only concern is NEC article 430.110 basically saying that table 430.250 to be used to get FLA which for a 1 PH 1/2 HP motor is 9.8A. This method would require 5 different breakers!

overkill because the motor nameplate FLA is 5 Amps, which would allow 2-20A circuits like you suggest.


What to do?

 

[hbiss]

Not the end of the world. If the breakers are close enough you could eliminate the disconnect switches. Sub panel for the boiler room? If you have 3 phase run two MWBC from that panel to the trough.

-Hal

 

[Ingenieur]

I would not consider those typ zone circ pumps
4 are the hw coils on ahu's, likely run on ahu demand or oa temp
the other is a dom hw circ loop, likely runs continuously

I would pair each pump with the associated ahu on a ckt
and put the dom hw on its own ckt

see if the specs/dwgs have a sequence of operation

 

[Ingenieur]

ot

I would have laid it out differently
a pump pair near the boiler feeding a hws and hwr loop thru the bldg
locate ahu's symetrically close to the loop riser
install a 3 way bypass control on each ahu
cycle the boiler off loop temp which would be proportional to load

 

[Designer69]

I would pair each pump with the associated ahu on a ckt
and put the dom hw on its own ckt

Only issue is the AHU's are 10.85 Amps each and if I have to calculate the pumps at 9.8A then I can't put both on a 20A ckt.

I guess this is going to have to be ugly and have a separate circuit / separate snap switch for each pump.

I'll check with the vendor tomorrow

 

[kwired]

Only issue is the AHU's are 10.85 Amps each and if I have to calculate the pumps at 9.8A then I can't put both on a 20A ckt.

I guess this is going to have to be ugly and have a separate circuit / separate snap switch for each pump.

I'll check with the vendor tomorrow

All at 120 volts?

I'd be pushing to use 240 volts if possible. Likely the motors in question are dual voltage - it may depend on any controls that you may not have a choice on (at this point anyway).

 

[Designer69]

yes that was my thought also to go with 240 but none of the zone controllers I found were rated at 240, only 120. But perhaps a bit more coordinating with Mech. engineer and boiler vendor is in order.

Thank You

 

[hbiss]

With 240V circulators you would use contactors with 120V coils controlled by the zone controller. But I'm pretty certain those 1/2HP circulators aren't standard for 240.

I think there are so many theories now as to how to do this that you need to get some input from the HVAC designer. Nothing has been said about the actual controller they want nor how it will be controlled by the building controls. Get a clearer picture then we can go from there.

-Hal