Should Manual Switches Be Installed on the High Voltage(ac) or Low Voltage Side(dc)?

[priorm]

I am trying to design my first electric system and appreciate the extensive knowledge of this forum.

I would like to use a brewtroller or BCS-460(2) to control a 30amp, two kettle, two pump setup. I would like the controller to manage both elements and pumps via SSR.

Most schematics that I see wire switches on the high voltage side of the SSRs. Why is this?

From what I understand, using switches on the low voltage dc side could eliminate the need for contactors, lower cost and simplify wiring. However, it would not account for SSR failure (while closed). Are the switches that are used of the high voltage side better quality than those used on the low voltage DC side?

Why do most schematics place the switches on the high voltage ac side instead of on the low voltage dc side?

 

[doug293cz]

It's a safety issue.

Based on your question, you should really consider getting help designing and building your control system from someone more knowledgeable with electrical systems.

Brew on

 

[orangehero]

Most designs based off of Kal's panel use a switch connected to a contactor's AC coil. This is to be able to shut off power in case of SSR failure as you mentioned. The commonly used selector switches are not rated for high amperage.

You can also use a high-amperage rated switch (240V 30A toggle switch can be purchased at home depot) instead of a contactor.

The safest design would use a contactor with a DC coil so you have low voltage on the switches.

 

[priorm]

Most designs based off of Kal's panel use a switch connected to a contactor's AC coil. This is to be able to shut off power in case of SSR failure as you mentioned. The commonly used selector switches are not rated for high amperage.

You can also use a high-amperage rated switch (240V 30A toggle switch can be purchased at home depot) instead of a contactor.

The safest design would use a contactor with a DC coil so you have low voltage on the switches.

OK. I understand that safety issue.

If the switch is on the high voltage side of the SSR, it can kill the downstream device it is controlling in the event of SSR failure. A switch on the low voltage side does not offer the same control and protection in the event of failure.