WE have just had our first electricity bill, and after doing some mathc,
have realised that by leaving the pond pump on all the time we are costing
our selves about £200 a year. I would like to put it on a timer so that it
comes on when we are here and off during the day. However it is on a RCD
plug in the shet, the power goes to the shed via a fused spur which is on
the RDC ring from the consumer unit. When you cut the power to the pump the
RCD needs resetting, so a trip to the Shed is needed to push it back on.
My question is, given the pump is on the RCD from the CU, can I do away with
the RCD on the plug, replace it with a normal plug and then use a time
Ye gods, that's about 300W by my calculation. I found a 155W pond pump that
claims to shift 1000 gallons/hr, which is a 2-gallon bucket every 7 seconds
or so. My mains can't fill a bucket that fast. How big is your "pond" ?
The height of the outlet pipe also has a lot to do with it
Maybe that 155W can shift 1000gallons/hr without pumping above the water
level, but I think you will find, as soon as you start pumping above it, the
output will fall quite quickly!
Another option, would to enquire about the cost of an economy 7 meter, this
gives you much cheaper electricity at night - It may work out cheaper (there
is an increase in the standing charge) you would need to sit down, and work
You would need to take into consideration other things that run at night
(Fridge, freezer etc..)
Also, other high current stuff that could be running at night rather than in
the day (Dishwasher, tumble drier etc..)
Non off-peak power also costs more. Using Norwebs figures from a while
Standing p/unit p/unit
Norweb Charge Peak Off Peak
E7 12.97 6.46 2.46
Domestic 9.39 5.94
To save Standing Charge 1.46 units per night
To save Peak Rate 0.21 Off Peak units per Peak unit used.
Dave. pam is missing e-mail
That's a swimming pool in most people's estimation :-) I see we are in
accordance on the consumption calculations.
I've had one too many beers to sit down and work out potential energy gains
or whatever. You shouldn't need to aerate ponds 24/7 though, so as you are
thinking of some way of putting this on a time-switch, some considerable
savings could be possible. What, er, *purpose* does the pond serve ?
How long is the run between the CU and the shed?
I have heard, that "long" runs can reduce the speed of an RCD - not sure
what long is classed as though :-/
In my house, I have a 30mA trip breaker in the house, there is a cable that
runs to a shed, I have installed a second CU there, this distributes to the
other shed, the garages and the greenhouse - this way I don't need to use
any plug in RCD's - and isolation of a particular building is as simple as
flicking a MCB :-)
Ok, i cant see 10M being a problem (I have runs in my house longer then
As long ans you have an RCD in the Conusumer Unit (30mA trip) then my
feeling is, loose the plug in RCD. (be sure to test the RCD in the CU by
pressing the little T button, just to be sure it works!)
You may want to install a small CU in the shed, at a later date, but I
wouldnt think it is striclty necassary - what is the capacity of cable that
runs from the house to the shed BTW?
Some RCDs stay latched if the power is removed. From my experience wil
a Screwfix extension lead with RCD plug, I would suggest that the
Screwfix RCD plug (16930) or adaptor (15623) should stay latched when
power is removed (the plug looks identical to the one on the extension
reel). This should solve your problem. Alternatively use a short
extension lead as
------------plug timer socket-------plug RCD wall socket
In answer to your RCD question - power consumption aside...
As you already have a main RCD in CU, then the extra "plug in one" is
serving no useful purpose, so I would recommend getting rid of it.
Should a fault occur it is a lottery which would trip first & both may
trip. These plug-in RCD devices often have a "feature" that can be
very annoying where they don't reset when the power returns. Built in
RCDs aren't like this.
So your timer idea would then work fine.
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