ECN Forum Forums General Topics of the Trade General Discussion Area sewer pump.

Had a sewer contractor out to remove an old pump and install new. He suggested another contractor to wire up new 230 VAC pump. All bad.

Concern I have is one hot leg is to pump at all times while other hot leg is turned on by level switch , Can this burn up 230v single phase pump motor?

1 hot leg to float switch through on/off switch. Switch turns pump on and off.
One hot leg through on/off switch
other pump wire to ground.

Thanks

"1 hot leg to float switch through on/off switch. Switch turns pump on and off.
One hot leg [directly -- and unbroken] through [the] on/off switch
other pump wire to ground."


1) You're describing what I like to call an "old school" trade practice. You'd be amazed at the stuff that was wired up that way. (Switching only one hot in a two pole/ two leg motor circuit.)

2) It's a very bad idea because:

a) It's wasting energy. The unswitched leg is constantly pulsing juice in and out of the motor windings. Even though it's not runnning, it's experiencing hysteresis losses thereby. For an ejector pump such a persistent bleeding of energy would entirely out match its primary function.

b) It's inconsistent with modern motor control logic. You're not going to catch a big price break because you're cheesing it on the number of switched poles.

3) Unless I miss my guess, you're going to need to install a safety switch within direct line of sight for this pump. The Code has really tightened up about disconnecting means.

Since my experience is biased by too much commercial practice, I might be too design-conservative.

I'm sure the maunfacturers drawing don't show the one leg control

Wow; so what would the shock feel like if you touched the motor thinking it was off while steadying yourself by holding on to the grounded water pipes?

If you have more than 1 hot conductor, you need to turn all of them on and off simultaneously.
Someone needs to replace the old level switch with a 2-pole level switch to make this happen and make it work properly (and safely). This was put into the Code many years ago...I guess your old school contractor either missed that, doesn't know or doesn't care.

Can this be explained further. How can energy be used with only one connection. There is no path of return to allow current flow to create any hysteresis effects.

f there is a disconnect present that opens all ungrounded conductors the motor controller can only open one

Thanks, Greg...you're right.

I was thinking of the OCP and enforcing what I read all the time in the Specs instead of the literal words in the Code.

IMHO, Teslas comment regarding a 'waste' of power is theoretical.

Yes, a double pole control device would be the 'spec' way, but a single pole is compliant based on the article Greg quoted.

Contractor isn't really saving much.

Visit SJE Rhombus for a modern, complete control panel.

Thanks guys, and yes it is wired that way in some of the pump diagrams. Speaking of old school, the 80 yr old contractor had alot of industrial experience..he was referred by the sewer guy with the pump truck. Had another worker bee doing all the work for him. Long and short when they cut the conduit back to the building control box, they never deburred the ID on the 2" conduit. Thus, insulation on wires gets cut. The startling thing is that its 208vac into the control box with a boost transformer taking it to 230vac. The 230 VAC supplied the control box at which point the breakers were down the line in the control box. Any transformers were acting as heat sinks. They wired the pump to the boost transformer at the terminal block where the boost transformer supplied the control box. They did not even have the lines to the pump fused..no breakers. They could have easily used the breakers in place from the old pumps. I got back to the office last Friday and dodged a bullet cause I checked on their work hours later and was presented with smoke on an auxiliary transformer that was almost boiling. I went back Saturday and met the 80 yr old...told him he almost burned up building..etc. I dug up dirt to conduit feeding pump and sure enough at conduit outlet ..all insulation burned off about 15 wires. I asked him where his wiring diagram was...ummm. None. Came up with a wiring diagram as stated in original post and put all back together. Working but I guess my concern I had was one hot leg to pump at all times. We did install 2 pole cutoff switch at sewer for pump. Also cutoff switch for alarm circuit. Checked amperage and it's pulling about 8 when pump on both legs for pump. I guess it will have to do for now.