Why Are There 40A Plugs On My Dimmers?

Why_40A_Plugs_webFor some years now, Jands has included 40A 3-phase plugs on its dimmers instead of 32A units. Although we have been doing this for a number of years, we still get many calls from surprised customers who find the 40A plug on their dimmer no longer fits the 32A socket in their venue.

So, why do we include 40A plugs when most venues have 32A sockets? Well, it comes down to maths and safety. The maths is the quickest to explain, so let’s start with that. Each dimmer is rated to 10A. There are 12 dimmers. With three phases of incoming power, that’s 4 dimmers per phase. 10A x 4 = 40A. AS3100, section 4.4.1 states that the plug must be “appropriately rated” for the application. A 32A plug would be underrated by 8A.

Ha! You say – these are “special purpose” outlets and generally protected by their own circuit breaker rated equal to that of the socket. So if I fit it with a 32A plug and plug it into a 32A outlet, all should be cool right? If I pull more than 32A the breaker will trip and so no problem.

Unfortunately, no. While you will not have any issue with a 32A socket, a 32A plug will also fit into a 40A or 50A socket. If you load up a phase of your 32A-plug dimmer with four 10A loads, and plug that 32A plug into a 40A or 50A outlet, that plug will be delivering 40A with no end in sight. This is way over the rating of the plug. The same argument applies for overrated circuit breakers, which some manufacturers fit to their dimmers in an attempt to minimise nuisance tripping. With a 13A breaker on each dimmer channel, in conjunction with a 32A or 40A plug in a 50A outlet, we could pull up to 50A, severely exceeding the rating of the plug.

The wiring rules are set up so that even your grandmother can plug things in and not put herself (or others) in danger. Taking all of this into consideration, we felt supplying 40A plugs and 10A circuit breakers was the only responsible thing we could do.

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