I don't think I have posted this before.
Read the EDS article first, to see the background. I have thought of this before: The EDS article speaks of 3x25A, but some countries (yeah, guess which
) use 3x16A.
Got a phone call from a friend yesterday, who had this problem. "The cooker rings aren't working nor is some of the heating." "Replace the broken main fuse"
It's impossible to balance a normal houshold on a small 3-ph system. No matter how you place the dishwasher, kitchen counter sockets, washing machine it only takes someone using the dishwasher, kettle and the oven to blow one main fuse. Sure, you can move them around but the only result is the fuse blowing when the washing machine is used instead.
Now this wasn't so bad if it weren't for the combination of phase-to-phase loads and single pole fuses which means that when a fuse has blown, the voltage is dancing around uncontrollably. When you turn on the cooker, the kitchen lamp goes on... Electronic equipment find itself on say 150V rather than 230V and go nuts. I've set of a fire alarm this way once.
On the other hand: Single phase is a very inefficient way of moving power and it causes problems with load balancing for the power company.
Striking a balance would seem nice, so here goes:
A 3-ph connection of less than 50A per phase shall count as single phase service of 2 x phase rating. For example a 3x50A service counts as one single phase 100A service. At the other extreme, a 3x16A service counts as one 32A single phase service.
In new install. Single phase should be used for up to 63A max. and three-phase from 3 x 32A and up.
{Jeering from the Brits: Why not 100A? From the Germanics: Heretic! Single phase is stone age! } Balancing 3x32A is possible as it allows two continous 16A loads to be run simultanously on one phase. Plus the kettle for a few minutes. 32A is enough even to run a normal sized cooker. On the other hand, 63A is still easy to wire and main breakers, RCD:s etc. easily fit a normal panel (16 mm2 cable).
Now: There is one more point for my system. The copper needed to run a 3x32A cable 3P+PEN is 4x6 mm2 = 24 mm2. 63A P+PEN requires 2x16 mm2 = 32 mm2. The difference in cost is probably outweigth by the more expensive 3-ph panel.
A 100A single phase serious is just silly, IMO, since balancing a 3x50A service won't be a problem. And by then you are using an incredible amount of copper: 2x25 mm2 or 4x10mm2, which probably makes the cost of a 3-ph panel less than the savings on the cable.
Next, I argue that main fuse/breakers shouldn't blow/trip unless in extreme and thus rare cases. Furthermore, I would like to mandate three pole breakers on 3-ph circuits to prevent uncontrolled voltages. These ideas, I think go hand in hand.
Hutch, can I use your bomb shelter? [This message has been edited by C-H (edited 01-08-2003).]