Beefcake Relay Control Hookup Guide
Saftey and Insulation
This product will potentially be used for mains wiring, so please read this section discussing how much space is required to prevent arcing.
There are a lot of standards out there, like the IEC standards, the UL standards, and the IEEE standards. These cover anything from test techniques, communication interfaces and of course safety. Each country requires a different set of standards for commercially released products, which is an experienced full time position just to make sense of.
The Beefcake Relay Control is a prototyping or component type thing and abides by no standards, but it was designed with safety in mind. Because it’s not a full product though, there is no guarantee that it will be used safely by you, the customer, so please be careful.
Making standards is good for business and compatibility but is also a business itself, so the standards can’t be found for free. However, creative Google searches can reveal the pertinent tables which have obviously come from the standards. Information from the standards have been boiled down to creepage and clearance calculatators for PCBs such as www.creepage.com. These can be used to come up with safe distances.
Play around with the creepage.com calculator, and see how the distances change. This section is intended to inform and not to scare. The terminology is a little odd so here’s a few terms that my demystify the calculator settings.
Functional insulation is intended to meet the lowest level of isolation for a given voltage. 250VAC is about 1mm.
This provides a level above nominal to allow surges and other common line disturbances to not cause a breakdown. For 250VAC, 2mm is required.
To make things safe for people to come in contact with, most standards require a second layer so that one can be damaged, and the isolation characteristic is maintained. Of course, this would be twice basic, or 4mm for 250VAC.
Reinforced insulation has the same insulative properties as double, but it is rated to be robust enough to not get cracks and pinholes such that it can be used in place of proper grounding.
Creepage and Clearance
Creepage is defined as the shortest distance between conductive surfaces along the surface of the PCB. It’s easier to conduct along the surface of an object than in free space, so this measure is the distance electrons would have to crawl to get from one conductive thing to another, along the surfaces in between. This will be farther than the clearance requirements.
Clearance is defined as the shortest distance between conductive things (like pads). Or, if there were an arc between the two things, what would the most likely path be?
What this means for the Beefcake Relay Control
Take a look at the PCB with strong lighting through it. The raw fiberglass of the board lets the light through but the copper doesn’t. It’s easy to see the traces and spacing this way.
There is a lot of distance between the high voltage and low voltage sides. There’s enough that you should be able to safely touch anything on the low voltage side, but please don’t. It’s good practice to avoid working with any circuit that is connected to mains.
Peeking inside the relay we can see a good distance between the low voltage windings and the high voltage contacts. This relay is rated to 2500VAC isolation between the coil and contacts, but manufacturing has statistical failure rates, and the user should always be wary of the dangers.