Controlling 120VAC and 24VDC Contacts with Single Relay Near VFD 3

[polareng]

I am designing a control circuit that will provide control contact for a 120VAC and the other contact will control a 24VDC circuit. Has anyone done this and, if so, should I be concerned?

To throw another variable into the design, the control circuit will be adjacent to a VFD which I am more concerned about transmitting EMI through the AC and affecting the DC signal or vice versa.

The reason I am somewhat concerned is because I read a precaution, some time ago, that AC circuits shall not be installed on the same terminal block(s) as DC control circuits, which I interpreted to mean track of blocks vice, that is, using the same terminal point on a block.

 

[itsmoked]

Not that I know of. It's done all the time. That's what a relay offers you, isolated contacts to do what you want with, as long as the relay's specs aren't violated in any particular use. Often they have poor DC specs, so just because a relay is rated 120VAC doesn't mean it's good for 42V DC, but then you probably realize this.

You can certainly mix AC and DC on terminal blocks too.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Good design practice in a cabinet maintains separation between low voltage control signals and mains power conductors. If you have room I suggest you do so, but if you are forced to mount them next to each other then it will be ok. Ensure your wiring is rated for the highest voltage present.

Curious: this forum is really for Solid State relays. Are you using a conventional mechanical relay or have you found a multipole SSR? The latter are uncommon.


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Scotty;
Uncommon unless you are working with semiconductor equipment then you can find them like flies on um, well, never mind.

Quad units are fairly popular.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[polareng]

I'm not sure how I got onto this specific forum, but thanks for responding anyway.

I'm using an Allen-Bradley 700-CFB310D and a 700-CFB220D to be exact. I would call it a multipole mechanical relay.

 

[jraef]

The conventional wisdom is to separate AC and DC circuits on terminal strips so as to lower the risk of someone accidentally applying the wrong power to a circuit in the field or while preforming maintenance. Of course, you always have the risk of connecting to the wrong circuit, but putting AC onto a circuit designed for DC can be an instant disaster. So that rule was made to reduce that risk. It also helps when troubleshooting so that you don't have your meter set for DC when you touch the probes to AC. Some people just use an extra tall barrier between the sets of TBs and/or maybe a different color block, i.e. blue for the DC circuits, but even that is not a "requirement", just good practice.