Motor Starter Required?

[freak111]

We are in the process of replacing our domestic water station control panel. Our current setup includes a lead and a lag pump, (460v 25 hp). We are wanting to wire the lag motor to a disconnect so that we can keep water pressure up in the building, while replacing the control panel. My question is.... do I need to use a starter on the lag pump, or can I wire it directly to the fused line voltage disconnect?
Appreciate the help.

 

[davidbeach]

Does your disconnect provide all of the code required motor protective functions?

 

[itsmoked]

Well. It's totally 'against the rules' to do that...

Would the circuit you hook it to have a proper disconnect capable of switching the starting current?

Will this be for half a day?

Will someone be standing next to the disconnect the whole time?

Will they be reading an ammeter while standing there so if the motor is seriously overloaded for any reason all the wiring associated with the motor won't melt and burn down the facility?

These are the questions you need to deal with if you want to hook things up improperly. Is it worth the legal and moral risk?

Remember that a motor that is overloaded can draw 2X, 3X, more than normal. The wiring won't be up for that.

Perhaps it would be better to carefully figure out what needs to be done to replace the stuff you want to, acquire everything you need. Lay it all out, go thru it in your head, considering any possible gotchas and then make your switch on an off time, like a weekend, avoiding the temporary kludge.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

If the fuses are properly sized, this could be done. But without an overload relay, you will have to reduce the fuse size such that it provides motor overload protection. Check with Bussman for fuse sizing. Also, your disconnect switch must have appropriate motor horsepower rating.

I don't recommend doing this and I certainly wouldn't want to run very long this way.

 

[jraef]

I don't believe you are able to find a standard fuse that will provide overload protection for a 25HP 460V motor anyway. I haven't checked, but I just don't think it's possible given the sizing rules and standard fuse sizes. Although that is listed in the NEC as being a possibility, that's because it is sometimes done on really small motors where there are more fuse sizes available, but it doesn't mean that anyone will make a fuse rated that way for something this big.

If it is just a manual operation anyway, buy a Motor Starter Protector, a combination device that is like a manual motor starter, only it also provides a lockable disconnect and the short circuit protection just like a fuse would.

Link to photo

 

[sslobodan]

Control panel hmm well I don't know what you guys in state means bu that exactly because here in Europe control panel is a place from which you only start gear (centralized point) All automatisation is somewhere in cubicles in facility, now on that cubicle you usually have the switch to start engine by hand. People nowadays are using PLC and Scada systems to start remotely and automatically but that principle with the override start on the cubicle is kept.
Now more practice advice If you don't remove the motor starter and his protection from its spot you can put a simple on and off push button permanently on the starter circuit and solve your problem. pump will run when you want and starter circuit does not take a lot of power so it can be done by any means (light switch even because start current is in mA maybe 20mA I need to look at PLC spec.) Another way to do it is to take peace of board (plain wood board) Mount the peace of rail on it attach it somewhere where no one will push it during the work. Disconnect current breaker (don't forget to disconnect power to both feeder and control circuit) move it to the board reconnect cable and start circuit supply and turn it on and of with that switch I mentioned previously. Remember that this job could take from 15minutes till 2 hours depending from your skill and place where starter and protection is situated in your cubicle. If you can't do upper things, the easiest way is to get 32 Amps starter and pray nothing will happen to an engine because fuse will not withstand the Amperage drawn from motor that can be 6 - 12 times bigger than nominal. (See their characteristics) and putting the fuse that is lets say 120Amps is very expensive and useless because it will not start if you have over current. Also what you should think of is that you need 3 phases for the work of an engine, so if you lose phase you lose engine without phase protection (Smoked away).
My advice to you is in general that if you don't have this stuff in cubical away from switch panel so you can start command circuit, shut down facility over night and hope for the best. (Do your job on changing switch board when you have least consumption)

 

[jraef]

Another problem I just thought of with using a fused disconnect alone to run a motor in bypass while the control panel is being worked on:

Even if you should be so lucky as to find a fuse size that will meet the NEC requirements for protection, fuses alone will present a very real risk of single phasing the motor. If only one fuse blows based on a running overload, as is going to often be the case, the motor will continue to run in a single phase condition because with only a fused disconnect switch in place, there is nothing to take the motor off-line until at least one more fuse blows. By the time that happens, your motor will most likely be severely damaged.

Using an MSP as I suggested earlier will ensure that in the case of an overload, all 3 phases will be opened.

 

[freak111]

Thanks for all the valuable input. Even though this is only a temporary setup I think I will set up the temporary motor using the current starter that is in the controller. We will only need the manual use of the pump intermittenly for about an hour, but at $1000.00, I don't want to take any chances with the motor. Thanks again for the responses !

 

[dpc]

Dual-element fuses can be used by themselves for motor overload protection. This is allowed by the NEC.

As I said, I wouldn't do it myself, but it does not violate the NEC.