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Posted By Topic: Double pole main switch with ripple control

Apr 03 2019 20:58

I recently came across a double pole main switch in a new build. One pole was labelled ripple which fed the hot water cylinder circuit. I've only come across the method where the ripple is on the load side of the hot water breaker with the neutral sleeved red etc and cant seem to draw out the circuit that works with the double pole main switch

Apr 03 2019 22:46

The reason for the double pole switch is to ensure that all power is removed from the installation when the main switch is turned off. The hot water feed originates at the ripple relay in the meter box and must be switched in the main switchboard.
The ripple relay could be incorporated in the meter if it is not a seperate unit in the meter box.

Apr 03 2019 23:20

It seems a bit odd to have an HRC fuse or an MCB to protect the hot water circuit in the meter box in a new build.

Maybe the sparky is old school.

Apr 04 2019 06:55

The HRC fuse or the circuit breaker is not protecting the water heater circuit. Its protecting the cable from the meter box to the switchboard. Often a 2.5 or 4mm. This cable is connected direct to the Street supply Via the meter and ripple control.
The double pole isolate is to isolate the 2 supplies at the switchboard.
This system has been around many many years on most networks and over the past few years the other networks are changing to it.

Apr 04 2019 07:14

Nalla, this is not the case in many new builds (in Christchurch).

Added expense of a 2 pole switch and a separate HRC or MCB in the meter box.

Apr 04 2019 09:00

Yes there are 2 totally different systems.
The one the OP is more familiar with uses the ripple solely as a control switch on the w/h subcircuit, electrically downstream of the main switch and subcircuit protection. Only used in areas where an "all inclusive" tariff is available; such that all power used comes at a price discounted to reflect the fact that some is ripple controlled. The ripple switch-pair is subcuircuit cabling, and needs no other protection.

The other system is for separately-metered supplies; in which case the single conductor from meter, through ripple, to MSB is a mains active. That's 2 active conductors, of different sizes, sharing a common N, and of course needing a 2-pole main switch.

The network and / or the energy retailer may require an overcurrent device in the meterbox; but it's NOT a requirement of "3000" in most cases. The "reason" is to provide overcurrent protection for the reduced-size mains. But overload protection for the ripple itself is provided by the fact it's a fixed load. Overload protection is provided by the (downstream) subcircuit mcb; and for 4 mm2, short circuit protection is provided by the usual 63A supply fuse (for 2.5 mm2, or for higher-rated supply fuse, you'd need to do a calculation). With all required overcurrent protection in place, the mcb/ fuse in meterbox is redundant; and the requirement for this protective device to be installed reflects old-school (lack of) thinking; and failure to understand clause 2.5 of "3000".

Apr 04 2019 09:16

As a variation, my abode has a three pole main switch, with separate feeds for the hot water tank, and the storage radiators. The two additional feeds go back to the meter box, but interestingly all three feeds are the same size copper. This is all original from the house being built in the 1980s I believe, in North Canterbury.

I wonder if the commissioning sparky did it so all the bases were covered, or when built there really were three meters in the meterbox.

Apr 04 2019 10:33

There would have been three separate meters, and either 2 ripples or a multi-switch ripple.

In fact the multiple "mains" actives don't all have to be switched by same main switch, can be a separate switch for each. But introducing multiple main switches in domestic situation isn't a clever idea.

people get used to the local "system", and finding a different way of doing things can be disturbing.
Some years ago I found a relocated house that had ended up with a dangerous "combi" system; through ignorance and failure to test. Originally wired as '"all inclusive" with 1P main switch and a switch-loop for the ripple.
Relocated to another area that used separate meters. New mains, new o/s metering, etc; so inspector must have attended.

So load side of main meter connected to large mains active, through to main switch in normal way.
w'h supply from Meter 2 to ripple, via fuse in meterbox supplying red core of original switch loop cable. All what you'd expect at that end.
But nobody checked the other end, where that active, now used as w/h mains, was still connected to the load side of the w/h fuse. Meanihg it wasn't controlled by the main switch. w/h subcircuit cable connected into same terminal so live at ALL times. Ripple control merrily switching; but w/h fuse fed from main switch kept w/h live 24/7.
Worst bit: with main switch off, ripple could back-feed through w/h fuse and liven entire house.

House had been like that for about 15 years.

That's two people who had their brains in neutral; including an Inspector who didn't deserve his ticket.