A Peek Inside A Typical British Residential Power Panel

No matter what field you’re in, it’s interesting and instructive to find out how others practice it. That’s especially true with electrical distribution systems, where standards and practices differ from country to country and even between regions. This tour of a typical British residential electrical panel is a great example of the different ways that the same engineering problems can be solved, and the compromises that always attend any design.

We’re used to seeing [Big Clive] tearing interesting devices to bits, but rest assured that this electrical panel remains largely intact as it gives up its secrets. Compared to the distribution panels and circuit breakers common in North American residential construction, the British consumer unit is a marvel of neatness and simplicity. True, the unit on display hasn’t been put into service yet, and things will no doubt change once an electrician is through with it, but the fact that everything is DIN rail mounted is pretty cool. [Clive] explains a few of the quirks of the panel, such as the fact that what looks like a main breaker is in fact just an isolation switch, and that there are a pair of residual current devices (RCDs), which we call ground-fault circuit interrupters (GFCIs) in North America, that also don’t act as circuit breakers, despite appearances. A stout bus bar is provided to link the RCDs to adjacent circuit breakers, forming two groups that are separately protected from ground faults.

[Clive] notes with dismay that the lugs of the bus bar can actually be inserted behind the rising clamp terminal on the breaker, resulting in poor connections and overheating. Still, we wouldn’t mind some of these concepts brought to panels in North America, which we covered a bit in a discussion on circuit protection a while back.

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Awesome Prank or Circuit-Breaker Tester?

Many tools can be used either for good or for evil — it just depends on the person flipping the switch. (And their current level of mischievousness.) We’re giving [Callan] the benefit of the doubt here and assuming that he built his remote-controlled Residual Current Device (RDC) tripper for the purpose of testing the safety of the wiring in his own home. On the other hand, he does mention using it to shut off all the power in his house during an “unrelated countdown at a party”. See? Good and evil.

An RCD (or GFCI in the States) is a kind of circuit breaker that trips when the amount of current in the hot and neutral mains power lines aren’t equal and opposite, which would suggest that the juice was leaking out somewhere, hopefully not through someone. They only take a few milliamps of imbalance to blow so that nobody gets hurt. Making a device to test an RCD is easy; a resistor between hot and the protective ground circuit would do.

[Callan] over-engineers. He used a 50 W resistor where 30 W would do under the worst circumstances. A stealthy solid-state relay switches the resistor in, driven by an Uno and a Bluetooth module, so he can trip his circuit breakers from his smartphone, naturally.
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Tripping Out: A Field Guide to Circuit Protection

My introduction to circuit protection came at the tender age of eight. Being a curious lad with an inventive – and apparently self-destructive – bent, I decided to make my mother a lamp. I put a hose clamp around the base of a small light bulb, stripped the insulation off an old extension cord, and jammed both ends of the wires under the clamp. When I plugged my invention into an outlet in the den, I saw the insulation flash off the cord just before the whole house went dark. Somehow the circuit breaker on the branch circuit failed and I tripped the main breaker on a 200 amp panel. My mother has never been anywhere near as impressed with this feat as I was, especially now that I know a little bit more about how electricity works and how close to I came to being a Darwin Award laureate.

To help you avoid a similar fate, I’d like to take you on a trip (tee-hee!) through the typical household power panel and look at some of the devices that stand at the ready every day, waiting for a chance to save us from ourselves. As a North American, I’ll be focusing on the residential power system standards most common around here. And although there is a lot of technology that’s designed to keep you safe as a last resort, the electricity in your wall can still kill you. Don’t become casual with mains current!

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