Septic Pump & Controller - Multiwire Branch Circuit and Disconnect Rating?

[sparky1967]

I'm wiring up a new septic system at a cabin in a somewhat remote location. The system consists of a pump in the septic tank and a controller panel for said pump. The controller and the pump each call for a dedicated 20A circuit. The main panel is at one end of the cabin and the pump controller panel and disconnect are mounted to an exterior wall at the opposite end. Is there any reason I couldn't simply run some 10-3 romex under the cabin (nice big crawlspace) if I use a double pole single throw breaker in the main panel? (I'm running #10 due to distance of run to prevent excessive voltage drop).

This seems to be acceptable per NEC but wondering if there's a good reason not to do this.

Also, I have not been able to find a disconnect rated @ 20 amps. It appears that 430.110 (A) and (A)(2) both allow a higher rating, so that I could use a commonly available 30A disconnect or even a hot-tub 50A disconnect which can be had cheap at Home Depot.

 

[cadpoint]

Depends on what the total load is of all the devices at the end.

I doubt that's it over 200' feet one way, 12/3 - and there's no reason not to consider 12/4 with the same breaker.

There are inserts for smaller fuses for inserting inside bigger fused disconnects.

 

[iwire]

I think it could be fine ........ but.

If the control panel contains alarm signals I would likely keep it entirely separate from the pump.

 

[Dennis Alwon]

I assume the controller is a sub panel where the pump and the alarm are on different circuits. If not then I think you have a problem. The ones I have seen and done required a 10/3nm and had the controls as well as 2a dp breaker for the pump and a sp breaker for the alarm.

 

[Joethemechanic]

Would not the handle tied breaker on the MWBC make the alarm inoperative should something on the other leg cause it to trip?

 

[cadpoint]

...The controller and the pump each call for a dedicated 20A circuit. The main panel is at one end of the cabin and the pump controller panel and disconnect are mounted to an exterior wall at the opposite end. Is there any reason I couldn't simply run some 10-3

Well then No! You need to address the requirements!

Would not the handle tied breaker on the MWBCmake the alarm inoperative should something on the other leg cause it to trip?

Good Catch!

 

[sparky1967]

Would not the handle tied breaker on the MWBC make the alarm inoperative should something on the other leg cause it to trip?

I knew there was a reason this was probably a bad idea. That makes perfect sense. Alarm needs to sound if pump circuit is tripped.

Pump is a small 120v single phase pump, so no 2p breaker required for it. Instructions for pump and control panel call for a 20a circuit for each. Code says I can't share a neutral unless breakers are tied together per MWBC rules, so guess that idea is out.

Total distance from panel to pump is approximately 110'. According to the calculations I've done, #12 would give me voltage drop in excess of 3% at that length. Am I doing something wrong?

As for the disconnect - can't see why I couldn't run any size I wanted as long as it's 20A or larger. 430.110 (A) and (A)(2) state that the "minimum" size of the disconnect should be 115% of the FLA. No maximum is given. All this is doing is disconnecting power to the pump and controller simultaneously, the purpose of the disconnect is not to protect the circuit. The protection for the circuits are provided by the breakers in the panel, right?

 

[Dennis Alwon]

Would not the handle tied breaker on the MWBC make the alarm inoperative should something on the other leg cause it to trip?

That is why I said if the unit is a sub panel feed by the 10/3 with it's own OCPD in the controller then you are okay. You don't want the alarm and pump to go off together. Of course it is possible the 30 amp dp will trip before the 20 amps in the box, but not usually. The units I have hooked up are designed that way.

Here is the kicker-- if the unit is mounted in the yard like many I have seen then you run into 225.30 and the mwbc problem. Either way you will be noncompliant unless you add a sub panel.

 

[Joethemechanic]

Pump stations I use to do had a ups protected alarm and dialer. There were a few nights I wish they would have failed. The only time I really ever worked on a small one was one for a single bathroom and sinks in a fresh water pumping station in Bordentown NJ.

That was a scary place. I walked into the basement and it was all rotten conduit, troughs, and god knows what all squirting water. I have no idea how long they were operating that way. I went back upstairs and found a way to get power to my pump that didn't involve that squirting mess of an electrical hazard.

 

[sparky1967]

Thanks for all the replies.

Will run two separate 10-2 to the disconnect and controller panel.

I'm thinking of using this disconnect. Says it's intended for an air conditioning unit, but don't see why it couldn't be used for this setup, and the price is right:
http://www.homedepot.com/Electrical...splay?langId=-1&storeId=10051&catalogId=10053

I was told by the guy who installed the septic tank and bought the pump and controller that the controller had OCPDs in it and I wouldn't need a separate disconnect but when I got out there to do the work I found that the controller panel did not have any OCPDs in it after all.

Thanks again!

 

[Dennis Alwon]

Thanks for all the replies.

Will run two separate 10-2 to the disconnect and controller panel.

I'm thinking of using this disconnect. Says it's intended for an air conditioning unit, but don't see why it couldn't be used for this setup, and the price is right:
http://www.homedepot.com/Electrical...splay?langId=-1&storeId=10051&catalogId=10053

I was told by the guy who installed the septic tank and bought the pump and controller that the controller had OCPDs in it and I wouldn't need a separate disconnect but when I got out there to do the work I found that the controller panel did not have any OCPDs in it after all.

Thanks again!

I don't think you need 2- 10/2. You probably can run a 10/2 maybe even a 12/2 and a 14/2 for the alarm circuit. So are you not going to disconnect the alarm cir.?

 

[sparky1967]

Yes, both the controller panel and pump need to be on the disconnect. That's why I linked to the one I did, as it's a 2-pole disconnect.

Distance from main panel to controller panel is approximately 80'. I don't know what the current draw of the controller panel is, but given that the instructions call for a 20A circuit for it, I'm worried that running #12 would end up with too much voltage drop. The fact it's a 20A circuit rules out #14. Hard to imagine that the controller panel would be much of a load, but I'd rather be safe than sorry. Not a lot of cost difference between 12-2 and 10-2 anyway.

 

[Dennis Alwon]

Yes, both the controller panel and pump need to be on the disconnect. That's why I linked to the one I did, as it's a 2-pole disconnect.

Distance from main panel to controller panel is approximately 80'. I don't know what the current draw of the controller panel is, but given that the instructions call for a 20A circuit for it, I'm worried that running #12 would end up with too much voltage drop. The fact it's a 20A circuit rules out #14. Hard to imagine that the controller panel would be much of a load, but I'd rather be safe than sorry. Not a lot of cost difference between 12-2 and 10-2 anyway.

The control circuit is a different circuit. You will need to separate the alarm cir. in the controller. This means a 14/2 is fine. A dp disconnect will not disconnect both the pump and the alarm. I am assuming that the pump is 240V as it normally is configured.

 

[sparky1967]

The control circuit is a different circuit. You will need to separate the alarm cir. in the controller. This means a 14/2 is fine. A dp disconnect will not disconnect both the pump and the alarm. I am assuming that the pump is 240V as it normally is configured.

The pump is only 120v as I mentioned earlier. this is a small system for a small structure so apparently a 240v pump isn't necessary.

The wiring diagram for this panel clearly calls for a single 20a circuit to feed the controller panel and a separate 20a circuit for the pump, no other circuits are shown. The alarm horn/buzzer/whatever it is is wired to the circuit board in the controller panel.

Here is the wiring diagram for it:
http://www.aquaworx.com/pdf/WiringDiagram_ipcS01.pdf

I'm sure that #10 is probably overkill for the control circuit but given the length of the run and the fact I don't know how much of a load that controller really presents, I'd rather be safe than sorry. The customer has no problem paying for the cost difference between #12 and #10 wire.

My main questions have been answered: 1) Can I share a neutral for the pump and controller circuit? -No, due to the requirement that both hot wires on that circuit must be shut off at the same time by a single throw breaker. 2) What rating should I choose for the disconnect? It doesn't matter as long as it's greater than 115% of the FLA of the pump motor.

Thanks for everyone's contributions, much appreciated!

 

[kwired]

Would not the handle tied breaker on the MWBC make the alarm inoperative should something on the other leg cause it to trip?

True common trip 2 pole breaker this is an issue. Handle ties do not take the other pole when only one trips (with many brands out there). It probably will shut down when attempting to reset the other breaker though because it will need to be moved to the full off position to reset it.

 

[Dennis Alwon]

True common trip 2 pole breaker this is an issue. Handle ties do not take the other pole when only one trips (with many brands out there). It probably will shut down when attempting to reset the other breaker though because it will need to be moved to the full off position to reset it.

That's a good point- I don't know that it is fool proof though. I seem to remember one that tripped that turned of the other. I would think the cutler Hammer brand where the trip is off would also switch off the other breaker if the one tripped.

 

[ActionDave]

That's a good point- I don't know that it is fool proof though. I seem to remember one that tripped that turned of the other.

I would agree. SqD handle ties are sloppy enough that a trip on one breaker may not take out the other, but I have seen it happen. All other styles that I have seen are such that there is no way they could not turn off the other breaker.

I would think the cutler Hammer brand where the trips off would also switch off the other breaker if the one tripped.

Yes, you can take the tie off a two pole breaker and it will still have common trip. You can switch them individually though.

 

[renosteinke]

Point of order: the load is the pump- not the panel. You don't need separate circuits for each.

The panel will take the feeder (that's what the circuit actually is) and divide it up into 'control' and 'power' circuits. The control panel rating refers not to how much power the panel needs, but to the largest pumps the panel can control.

For a disconnect ... the panel will have disconnecting means for the pump as part of the panel. If you want to instal an additional disconnect, I reccomend the Square-D "QO200TR." This $12 disconnect is rated for 60 amps with the included QO-style SWITCH, but you can readily replace that switch with a QO breaker of whatever rating you like. You can even use two single-pole breakers.

Why might you want to run an MWBC anyway? Well, it's been my observation that there always is a need for 120v at the pump house- whether for lights, or a convenience receptacle, whatever.

A typical arrangement might be a 30-amp 2-pole feed to a disconnect with two 20-amp single pole breakers. One breaker would feed the pump panel, and one would be for the convenience of the owner.

 

[Dennis Alwon]

Why might you want to run an MWBC anyway? Well, it's been my observation that there always is a need for 120v at the pump house- whether for lights, or a convenience receptacle, whatever.

A typical arrangement might be a 30-amp 2-pole feed to a disconnect with two 20-amp single pole breakers. One breaker would feed the pump panel, and one would be for the convenience of the owner.

There is no pump house. The controller is on the cabin building , as I understand the op. zthe septic pump is usually underground in a concrete manhole. Generally we run the wires to the pump and install a 4x4 there with the controller mounted to it.

 

[renosteinke]

Correct you are ... for this post. I was trying to give a more 'generic' reply, as I have seen this query come up many times at other forums.

A typical chain of threads in "Forum X" will start off with 'how do I get power to my pump / well/ shed?" The OP always has an extremely limited need to address. "Minimalist" answers follow.

Six months later, the OP is back, wanting to add a light, or a receptacle, or whatever .... and, all of a sudden, they need the 'unnecessary' neutral or second 'hot.' Oops.

For this thread ... well, pumps- and their controllers- come in several varieties. The OP is speaking of one pump, but it's quite possible that he'll want to add a second later. Heck, if it's just one pump, he doesn't need a 'control panel' at all; it all comes down to his specific equipment.

Another common arrangement -especially for the single-pump residential set-ups - is for there to be a completely separate alarm. He'll need a receptacle or circuit for that.

This is the type of job that seems always to grow ....