HELP 2 SSRs used on 230V motor--do I need to protect against 110V?

[Mark Main]

For my boiler heat at home I have a 230V 1.75A AC water circulating
pump (GrundFos UP26-116F)
Here are the specs for it:
http://www.us.grundfos.com/Web/Down...D6924665160825691B006361ED/$File/Up26116f.pdf


Unfortunately the pump runs 24x7 during the heating season even when
all 4 of the thermastats are open (which shuts down each of the water
valves).

I have 2 Omron SSR (DC-RR010), here are the specs.

http://www.sure-electronics.net/DC,...ays SSR 24-480V AC, 25A SSR user's manual.pdf

I want to use the SSRs for the 2 hot leads of my 230V motor, which is
simple enough... but what happens if one of the relays fail? Does the
motor have built in protection of it's only receiving power from one
of the power leads (in otherwords it becomes 110V), or do I need to
build a circuit that protects the motor?

And if so, then how?

Thanks.

 

[Mark Main]

The motor needs only one lead switched to control it.  You
need a mechanical 2 pole disconnect switch to isolate both
lines for maintenance, if you do not provide a separate
circuit breaker for this small motor.  And you need fuse or
circuit breaker protection in both lines to account for the
possibility that either side might short to ground.  But I
don't think you need a 2 pole control relay to turn the
motor on and off.

--
Regards,

John Popelish- Hide quoted text -

- Show quoted text -

The circuit breaker at the service panel is a "dual breaker" that
covers both circuits going to the motor... so, if only 1 of these
lines is hot and the motor is turned on, will that trip the breaker?
It was my assumption that all 230V motors would be designed so that it
won't burn out if only 1 of the circuits is hot... and if this is
true, then it seems like I'm protected two different ways.

 

[whit3rd]

[about a 230V appliance]

The circuit breaker at the service panel is a "dual breaker" that
covers both circuits going to the motor... so, if only 1 of these
lines is hot and the motor is turned on, will that trip the breaker?

There's a misconception buried in there: a circuit
is a full current-out/current-return path, and the usual
230V appliance has only ONE circuit. It has two
LIVE WIRES, not two circuits.

A turnoff switch needn't disconnect all live wires from
the motor to perform its function. One SSR will control your
motor (or water heater). To make the wiring safe, however,
your circuit breaker DOES disconnect all live wires.
In case of fault, to prevent fire, that's useful. In case
you want to work on the wiring, to prevent shock hazard,
it's useful.

The SSR (solid-state relay) isn't reliable and fail-safe
the way the circuit breaker is intended to be, so it
cannot do the same job as the circuit breaker in any case.
Thus, "double SSRs" isn't useful.

 

[Jamie]

The circuit breaker at the service panel is a "dual breaker" that
covers both circuits going to the motor... so, if only 1 of these
lines is hot and the motor is turned on, will that trip the breaker?
It was my assumption that all 230V motors would be designed so that it
won't burn out if only 1 of the circuits is hot... and if this is
true, then it seems like I'm protected two different ways.

If its single phase ( 2 wires only from service) you need only to open
one side. Your service should have a dual breaker for this line so even
if the motor should short to ground the lead that stays connected, it'll
simply popped the breaker for you in which case you would need to
service the motor any ways.

P.S.
You may want to consider a motor starter contactor over using a SSR.
they come with various selections of coil voltages to energize the
relay. You can even op for a motor over load on the starter.


http://webpages.charter.net/jamie_5"

 

[PeterD]

The circuit breaker at the service panel is a "dual breaker" that
covers both circuits going to the motor... so, if only 1 of these
lines is hot

Why would one of the lines at the box be hot, and the other one not?

and the motor is turned on, will that trip the breaker?

Why would it trip the breaker? Unless there was a short, the motor was
locked rotor, or some other failure.

It was my assumption that all 230V motors would be designed so that it
won't burn out if only 1 of the circuits is hot...

Why are you saying "1 of the circuits", as if there were two? There's
one circuit, a 240 v two wire feed. That other, third wire, is a
ground.

and if this is
true, then it seems like I'm protected two different ways.

I'm not sure what you are protected against!