With the contracting out of a lot of electrical work to third parties, the general standards seem to slip more, as the quotes are lower, and or (in)competency of people working on the network. A lot of matters are re the simple wiring of contactors to control streetlighting and hotwater, The ommision of phase fuses in circuits or inadequate sized cables. These photo's were taken from a distribution transformer TB 994, in Oteha Valley Rd, Albany, New Zealand. Relay was replaced by persons unknown, no DIN rail in grey box, relay fallen out on to Neutral bar, 32 Amp HRC fuse desintergrated, was still live and fused via a 250 Amp DIN fuse.
There's the slimy little culprit in the foreground, so slow he hasn't fled the scene of the crime yet! This would never happen here- he would have been sautéd, stuffed with garlic butter and served with a nice bottle of merlot!
I've seen several references to "hot water" circuits across this forum. Does this mean what it sounds like -- that the power utility provides different service drops for hot water heaters than for other loads? Why?
Where I grew up in the rural suburbs of Philadelphia we had a seperate meter and 30a service disconnect just for the water heater. This was commen in many neighborhoods served by PECO. It also had a tamper proof timer attached to the meter box. The idea was you paid a lower rate for electric water heat as the unit could only operate on non-peak hours.
My chauff-eau holds 200 litres [c.50 gallons] and is a 2kw immersion-element water heater running soley on cheap rate 230VAC supply, presently about 7 centimes per kwh. Models range from 50 litres and up. I have 2 meters, the cheap rate automatically switching for all consumption in the off peak times, 1am-7am and 12pm-2pm, and times which, incidentally, I can choose within limits. During off peak only, a live [hot] signal appears from the off-peak meter and feeds to 3 breaker 'units', for want of a better description. a] A 10A breaker to protect the signal/relay circuit. This is the lowest rated breaker now available in France, [ it used to be a 5A fuse in the old days]. b] A 16A [or as necessary] breaker to protect the immersion element circuitry. c] The switching device itself, basically a 20A rated relay arranged so that cheap rate is only normally used for water heating, and occupying one breaker space. This has a 3-position slider switch to enable OFF/AUTO/OVERRIDE selection, the latter so you can heat water during normal rates if necessary. The slider automatically returns to the cheap rate position on getting the pilot signal, so you don't have to remember to switch back to auto from manual, which is neat. Chauff-eaux [plural] are almost universally used here for domestic hot water generation, as it is by far and away the cheapest option. It is reliable, cheap to install, totally automatic and the insulation round the cylinder is so effective it will keep stored water hot for at least a week with no power. And since France has 75% nuclear*/hydro generation, off peak is now cheaper than gazoil per kwh considering overall efficiencies.
* 58 nuclear reactors in 14 power stations.
[This message has been edited by Alan Belson (edited 05-03-2006).]
Gus, what you are describing is known as an "off-peak" service. It is the same service drop as the main service,, but the POCO adds an additional meter to the drop for water heaters and electric heat. This meter is either clock driven, or wireless. The idea is to turn power to these loads off at given times, to reduce deamnd on the whole system during peak hours. In return of allowing them to shut these loads off, during demand times, they in turn bill you for this use at a lower rate...
Dnk, You are correct. Power companies here limit the operation of storage Hot-water cylinders by what is known as a Ripple Control system. Effectively all it means is, the PoCo induces a series of tones (anywhere from 500 to 1500Hz) into the supply lines to open and close a ripple relay (actually a type of impulse relay) at each customers installation, thus controlling the amount of time the load is energised. It is generally referred to as "Night-Rate" as the supply is usually switched on at 11pm and switched off again at 7am. Night-store heating is also controlled in this manner, except this requires an extra meter in the meterbox and an extra channel module in the ripple relay itself.
If I'm reading correctly, there is only one drop to each residence, but a PoCo-controlled relay enables power through a second meter for reduced-cost night-time loads.
This, of course, raises more questions:
1. Why not switch ALL loads to the night-time meter? Unacceptable dropouts during the transfer (which don't matter to a heater)?
2. Why then would there be a "hot water" contactor in a distribution transformer cabinet that presumably feeds multiple customers?
It's interesting to see how the rest of the world encourages load demand leveling. (Quoting comedian Eddie Izzard at a U.S. performance: "You do know there are other countries, yes?") The dual-rate meters I've seen photos of in this forum make a lot of sense to me.
Here in Southern California, I understand that some utilities offer a discount to customers who allow them to install remotely-controlled contactors that shed high-power loads (e.g., air conditioning) at peak demand times.