A couple magnetic starter/relay questions

May 26, 2004 7 Replies
J

I have a magnetic starter on my table saw. It consists of a on(momentary close)/off(momentary open) switch and a 4 pole relay. On of the poles fused closed so I used another pole. Since then it has worked, but has been flaky. I figure it is time to replace the relay. As long as I am doing that, I am changing from 120v to 240v. I bought an Omron 07J 4A B relay.


1) On the old 120v relay, a hot wire went to a pole and then to the Off switch. The other wire to the off switch is a neutral. Presumably (since this relay has a 240v coil) I run a hot to the switch instead of the neutral. But do I have to run it to the relay first, so that both hots run through the relay, or is just one adequate. It can't hurt to do both, but I can use the old wiring as is if I just do one. Are both necessary? (yes, of course I will run each hot to the motor through the relay)


2) There were no instructions with the relay. It has 10 contacts:



13,14,23,24,33/31,34/32,43/41,44/42,A1,A2. Looking at their website, I "think" that the coil is A1,A2 and all the others are NO poles. I "think" the weird double numbering is because they use the same mold to make relays that have 1 or 2 NC poles. Does this seem right?


3) The relay has screw terminals. Rather than fuss with trying to get wires under them, I will crimp connectors on to the wires and just stick the connectors under the screws. That is okay, isn't it?



Thanks.


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E

With a 240 volt relay coil, the coil must be connected to both hots. All you need to do is change the plug so that it connects (properly) to a 240 receptacle. That will automatically put a hot where the neutral was.

Why not post the url so we can see the diagram you refer to?

Yup.

Don't forget to re-wire to the motor terminals for 240!

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G

Answer: NEC 2002 430.84 Need Not Open All Conductors. The controller shall not be required to open all conductors to the motor. Exception: Where the controller serves also as a disconnecting means, it shall open all ungrounded conductors to the motor as provided in 430.111.

Anwser: This is manufacturer specific.

Answer: You can install the wires under the screws or use terminals. Terminals are very expensive so many contractors skip the terminals to save on material and labor costs. As a matter of fact, I know one contractor that instructs electricians to not use terminals for these very reasons, and they build UL listed panels that do not use terminals.

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I

Magnetic STOP START Controller Overload ---?--- Coil Contacts

----O__|__ O---|---O O--|--------()()()()()---------|\|---|\|----- | | | | ------| |----- Controller Auxilliary Contact

Controller Contact Thermal Device L1-----------| |------------~~~~~~~~-----------MOTOR------------L2

Here is a standard circuit for a motor controller. In your case, L1, and L2 would be 220 volts, and so would the feed to the stop button and overload contacts.

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J

So, I wasted my money buying a 4pole relay when a 2 pole would have done the job. Is that about it?!

Thanks.

on(momentary

Contacts

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I

Actually, no; you do need 3 controller contacts: two for the motor -- since it is a 220 volt motor, and one for the auxilliary contact. I have revised the diagram to indicate the extra contact for the motor.

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E

While it is better to interrupt both hot leads to the motor, it is not required. See NEC 430.84 as G.Newton pointed out.

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G

Controller

Only one leg of the motor is required for controlling the motor if the controller is not used as a disconnect per code.

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