Transfer Switch -- Electrical Advice Needed

[Distant_Shaws]

I am all for simplicity and Have a 4 position switch just like misssheary

My swatch ore for shore power, generator , inverter or off positron.

Much simpler than an automatic change over or contactor that can go wrong at the worst time possible

[Jammer]

Originally Posted by Distant_Shaws

I am all for simplicity and Have a 4 position switch just like misssheary

My swatch ore for shore power, generator , inverter or off positron.

Much simpler than an automatic change over or contactor that can go wrong at the worst time possible

Any switch can fail. MTBF data for contactors is no worse, and in many cases, better than that for manual, mechanical switches. The main reason that contactors fare better is that the opening and closing action of the contacts is rapid and predictable, while manual mechancial switches must use rotary mechanisms that produce arcing, limiting contact life.



But the main problem with manual switches is that the wiring has to come to the switch. Often this results in compromises: the switch may be placed in an inconvenient location to keep the wires shorter, or the wires may be longer than would necessary with a contactor, or both. The wiring for a large manual switch also uses up more panel space, something often at a premium.

[s/v Jedi]

Originally Posted by Jammer

Any switch can fail. MTBF data for contactors is no worse, and in many cases, better than that for manual, mechanical switches. The main reason that contactors fare better is that the opening and closing action of the contacts is rapid and predictable, while manual mechancial switches must use rotary mechanisms that produce arcing, limiting contact life.



But the main problem with manual switches is that the wiring has to come to the switch. Often this results in compromises: the switch may be placed in an inconvenient location to keep the wires shorter, or the wires may be longer than would necessary with a contactor, or both. The wiring for a large manual switch also uses up more panel space, something often at a premium.

All true, but with all my background in process control electronics I still opted for a manual switch. The reason is that it is your brain allowing you to switch when there is no load at all; that it is the muscles in your fingers powering the switch and that it provides ample room on the panel for some graphics showing how things are wired

The wiring on the switch in the picture is just the output side: it is three separate switches so you have to parallel the outputs yourself. This is a 4-position, double pole, 63A switch.

[Matt Johnson]

Originally Posted by s/v Jedi

All true, but with all my background in process control electronics I still opted for a manual switch. The reason is that it is your brain allowing you to switch when there is no load at all; that it is the muscles in your fingers powering the switch and that it provides ample room on the panel for some graphics showing how things are wired

The wiring on the switch in the picture is just the output side: it is three separate switches so you have to parallel the outputs yourself. This is a 4-position, double pole, 63A switch.

Now that is nicely done! Love it.

[Statistical]

Semi OT but what are those 3 displays on the left s/v Jedi?

[Statistical]

Originally Posted by Jammer

But the main problem with manual switches is that the wiring has to come to the switch. Often this results in compromises: the switch may be placed in an inconvenient location to keep the wires shorter, or the wires may be longer than would necessary with a contactor, or both. The wiring for a large manual switch also uses up more panel space, something often at a premium.

Exactly. That is why contactors exist in the first place. Imagine how much of a pain in the butt installing a central house AC would be if you needed to run 240V 50A wiring through the house and to the thermostat. Instead your thermostat sends a low voltage signal to the contactor on the compessor (outside unit) which switches that 240V 50A for you.

[s/v Jedi]

Originally Posted by Statistical

Semi OT but what are those 3 displays on the left s/v Jedi?

They are energy meters: https://www.amazon.com/gp/product/B07JB9B2QL

[captstu]

Home Depot and nearly everyone else in the business sell a double pole double throw center off 30 amp rated switch for about 20 bucks.

It makes a perfect transfer switch, absolutely failsafe, UL rated, and simple to both install and operate.

All the others are more complicated and less reliable.

[Jammer]

Originally Posted by captstu

absolutely failsafe

They're not. They can fail closed if the contacts weld together, and then it is possible to connect the two sources together.


The mechanical interlock in Dockhead's OP physically prevents the second set of contacts from closing unless the first set is open, because there is a physical interlock between the armatures of the two relays. If a contact welds shut then the interlock will not release.


Similarly, the drum switches sold by Blue Sea and similar vendors, have a rotary cam that forces the contacts open. If the contacts weld shut, the cam won't turn and it is therefore impossible to close the connection to the other source.


In my experience the DPDT light switches are in fact quite reliable but that is not the same as being failsafe.