[safety] Phase selector relay

Sep 13, 2021 Last reply: 4 years ago 7 Replies

Rate this thread:

Piotr Wyderski 4 years ago

Hi,

I need to connect a single-phase load to one of two available 400VAC phases. Permanent on state is a safe condition, the load behaves like a light bulb. Therefore, simple contact welding is not a safety hazard. Perhaps the only catastrophic scenario would be a short between the phases. Will a regular SPDT relay with sufficient dielectrict strength do or do I need a special relay? In other words, is it realistic that the contacts become welded in such a way that energizing/de-energizing the coil would bend the contact block sufficiently to cause an inter-phase short, either metallic or via plasma arc?

We are speaking of 3A semi-resistive load and the switching is rare.

Best regards, Piotr

Vote

John Larkin 4 years ago

Fuses or CBs would be prudent.

Vote

Lasse Langwadt Christensen 4 years ago

mandag den 13. september 2021 kl. 21.13.49 UTC+2 skrev Piotr Wyderski:

only need one?

formatting link

Vote

Piotr Wyderski 4 years ago

Two. Thanks, but this DIN behemoth is way too big and the phase selection algorithm would be more complex. I need a steerable coil.

I am not sure if in an application like this I should consider a force-guided relay with the NO and NC contacts placed in separate compartments or if a regular relay would do.

Best regards, Piotr

Vote

Piotr Wyderski 4 years ago

Sure, but it would be best not to trip them in the first place.

Best regards, Piotr

Vote

Jan Panteltje 4 years ago

On a sunny day (Mon, 13 Sep 2021 22:37:18 +0200) it happened Piotr Wyderski snipped-for-privacy@protonmail.com wrote in <shocq8$vbj7$ snipped-for-privacy@portraits.wsisiz.edu.pl>:

Triacs?

Vote

Piotr Wyderski 4 years ago

2V drop and no physical gap. A relay has some advantages.

Best regards, Piotr

Vote

piglet 4 years ago

Do not wire the phases to opposite fixed contacts of a change-over. This is actually prohibited in some aerospace high rel specs. The problem is an arc developed as the moving contact breaks from one fixed contact can be stretched across to engulf the other fixed contact.

Better to use an NC/NO contact set or two separated contact sets.

piglet

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required