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Switching mains power for Shcuko type plugs with no polarity in a control panel

Switching mains power for Shcuko type plugs with no polarity in a control panel

Switching mains power for Shcuko type plugs with no polarity in a control panel


We are revising a control panel for a machine to work with 110VAC or 220VAC. The machine plugs into a wall outlet. The panel uses 3 DIN mount switching power supplies. In the US, we can use single switches or breakers to cut power to each power supply because the hot and neutral are polarized. We can be sure the hot is switched.

In European applications, some plugs like the 2 prong Schuko can be installed either way. This has the effect of reversing the hot and neutral with the switch only breaking the neutral.

To cut power to the entire machine, we have a 2 pole key switch that can break both the hot and neutral regardless of orientation.

It seems we will need some type of 2 pole switch for each power supply to ensure we are cutting both. I have 2 issue with that. The first is cost and the second is safety.

A brute force method is to use an IEC power strip with cords and plugs to each power supply. Unplugging a power supply is a certainty that both lines will be disconnected. Our space is tight but this is still feasible.

What I want to know is how are industrial control panels that are plugged in rather than hard wired set up to address this? I struggle with issue since European safety standards are so strict yet polarity issues are allowed.

RE: Switching mains power for Shcuko type plugs with no polarity in a control panel

Why not use two-pole breakers instead of the single-pole breakers?

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RE: Switching mains power for Shcuko type plugs with no polarity in a control panel

Two pole breakers or switches are an option. Cost is a factor but we are using a 2 pole key switch to cut main power. My concern lies with widespread use of a plug design that allows a condition where only the neutral is switched. That seems to be a high probability in residential applications as well.

RE: Switching mains power for Shcuko type plugs with no polarity in a control panel

Code compliance requires two pole breakers.
Plugging into a power strip implies flexible cords.
Flexible cords are not approved for this type of fixed installation.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Switching mains power for Shcuko type plugs with no polarity in a control panel


Let me back up and provide a little more background. This may help clear up some of my questions.

Our equipment is essentially a vending machine although it performs a different function. It is certified to UL751 for US and has CSA C22.2 certification for Canada. It plugs into 110VAC wall outlets and has a GFCI plug. We have never hard-wired our equipment to power, it's always plugged into a wall outlet.

Historically, we have used open chassis type power supplies to provide DC power (5,12 & 24 VDC) to components in the machine. With all of the supply chain challenges over the past few years, we have had to find alternate power supplies. This has some complexities. First, the mounting pattern for the power supply may be different which requires an adapter plate. Second, the output connection methods are never the same. This is the bigger issue since it requires alterations to our wire harness including different pins, headers and different orders for wires on the outputs which then require alternate configurations to schematics.

We are exploring the use of DIN power supplies for the following: 1. They mount on DIN rails so no fasteners or adapters are needed 2. They use screw terminals so no pins (other than ferrules) are needed and wiring simply requires putting the correct wire in the correct terminal. 3. Alternates are more available and because we are using dedicated voltage power supplies, they are more available than multiple output chassis type power supplies. 4. We can eliminate a lot of "wall wart" power adapters. 5. Because the DIN power supplies are self contained, we don't have to fabricate additional covers to protect against accidental contact with mains terminals.

Any changes we make will be subject to recertification per UL751 and I will have our testing lab review the configurations.

Going back to my original post, for US and Canada, we are always certain the hot and neutral wires will be correct because of plug polarity. Overseas use, depending on the plug type could result in reversed hot and neutral coming into the machine.

Double pole switching may be required and that may be something we need to consider when designing for overseas use.

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