Separate loads on multipole breakers. 1

[itsmoked]

I have a couple of reagent pumps in a water filtration plant. I don't really want one running while a second isn't running so I'd like to run them on individual poles of a ganged breaker in my control panel. They're both about 2A 1ph 120V pumps. I can't think of any proscription on this. Anyone else?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rhatcher]

I don't see a problem with this. I assume that the reason that you want to use two miniature breakers ganged together instead of simply wiring both motors to the same (still miniature) breaker is because the breakers are providing the overload protection (?).

 

[itsmoked]

Thanks rhatcher.

Yes, though being 1/3hp 1ph motors I think they have internal thermal protection anyway. I'm thinking a tripped breaker is less puzzling than a "sporadic motor".

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SceneryDriver]

I may have missed something, but what prevents you from placing both motors on one single-pole breaker? At those amperages, a 10A breaker would be more than adequate, and would save some space in the panel.


SceneryDriver

 

[itsmoked]

Hi Scenery,

Nothing prevents me from putting both motors on a single(pole) breaker. I absolutely could place them on one breaker. However a two pole 2A breaker will provide some motor OVERload protection. Without it a motor might thermal itself off leaving the other motor running. Instead of jamming in a bunch of unreacted chlorine or ferric chloride because the other motor continues, the two-pole trips, stopping the 'other' reagent. This provides a bit of protection from making bad water.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Keith.
I would use an individual overload relay for each motor but use a common contactor for both motors. If either motor trips, both stop and the tripped O/L will indicate the source of the trip.
The "Cadillac" system would monitor the flow from each motor/pump but we all don't drive Cadillacs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SceneryDriver]

Keith,
That makes a tremendous amount of sense. "Unreacted chlorine" is a very good reason to get things shut down.

Are you planning on using a 2-pole 2A breaker, and feeding both sides from one hot leg? Just curious.



SceneryDriver

 

[itsmoked]

Man Bill, you've "Cadillac'd" this baby! You've taken a $10 dual pole relay into about $150.. These pumps are identical if they where different your method would probably be the only solution.

Scenery; When making water you aren't supposed to get over about 1ppm chlorine. When injecting ferric chloride the chlorine reacts with it. You have to increase the chlorine to something like 5ppm so once reacted you still have the 1ppm. If the ferric chloride stopped you'd find yourself delivering 5ppm water which can cause burns.

Normally you'd be monitoring the individual flows and arrest the system at a loss of any reactant flow. Unfortunately there doesn't appear to be any sensors capable of monitoring the flows we have to work at.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Sorry. I've been working in the oil patch for the last couple of years. I must have lost the "economy mode thinking that was the norm during my years in Central America.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[controlsdude]

I do not think 1 pole tripping will make the other pole of the circuit breaker to open with it. I think its a mechanical problem if you just want 1 pole to trip and pull the other with it. I tried to do this before, so asked the rep this question, and the manufacturer rep said that using a 2 pole will not trip on 1 pole going open based on 2 devices connected to each leg of a two pole breaker.

You could put a aux contact on the circuit breakers, have this going to a controller to open a contactor above both circuit breakers. I think Bill is right for a different reason, even if its more expensive.

 

[waross]

Can you put the pumps on the same motor with double ended shaft?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

dude; I'm pretty sure all double pole relays trip their neighbors.

Bill; They're reagents that you need to independently set so I don't think so.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MikeHalloran]

One downside I can see is that an average installer, on seeing a two-pole breaker, is likely to wire it up to 240V. ... and _then_ read the instructions after the smoke comes out.



Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

If the loads are connected properly that won't matter Mike. Each device should be connected from one pole to the neutral and get 120 Volts whether the supply is 120 Volts, 208 Volts or 240 Volts

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sibeen]

I do not think 1 pole tripping will make the other pole of the circuit breaker to open with it.

So what does a three pole ganged MCB do if one of the phases has an overcurrent? How does a three phase breaker feeding three different boards decide that the other two phases are OK?

It trips.

 

[ScottyUK]

I am fairly sure the trip times are different for a single phase overload to those for a three-phase overload of the same magnitude.

 

[waross]

A two pole breaker MUST trip on an overload on either pole and it will trip both poles.
Two single pole breakers with a handle tie may not trip both poles.
Many breaker are trip free. That is the breaker will trip even if the handle is held in the closed position. So with two single breakers ganged, there may not be enough force exerted by the handle of one pole to trip the other pole before the "trip free" feature kicks in.
Moral; If you want to be sure use a two pole breaker, not two single pole breakers with a handle tie.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[controlsdude]

I think Bill's explanation is what I got from the circuit breaker rep. Thank you for the explanation.