RCD's And Timer Switches

[Mike Hibbert]

Hi All,

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 switch?

Cheers

Mike

[John Laird]

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" ?

[Sparks]

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!

Sparks...

[Sparks]

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 :-)

Sparks...

[Mike Hibbert]

The pond is about 20m2, and the pump needs to pump up about 1.5m. It is a

250W pump, by the way.

Dunno how much water it shifts though!

Cheers Mike

[Mike Hibbert]

thats a good idea, I may try that (in the future - need to get other jobs sorted first!)

the run to the shet is probably about 10m

cheers Mike

[Sparks]

Ok, i cant see 10M being a problem (I have runs in my house longer then that!)

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?

Sparks...

[Sparks]

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 it out!

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..)

Sparks...

[Sparks]

can I do away with

Another question...Is this pump purely for decoration, or is it part of a filtration system in a pond full of fish?

Sparks...

[Dave Liquorice]

Non off-peak power also costs more. Using Norwebs figures from a while ago: 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.

[Mike Hibbert]

Hi,

No, it's purely decorative! The pond is only about 12" deep, too shallow for fish.

cheers

M

[Malcolm Race]

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

Malcolm

[Sparks]

That's ok then ;-)

If it were for a filter, you wouldnt want to be turning it off!

[Mike Hibbert]

Thanks to all who replied, got it sorted now and by my calculations I should save about £150 a year.

[John Laird]

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 ?

[Mike Hibbert]

Well basically, is serves bugger all purpose (except giving the cats somewhere to drink from!), but it looks nice!

[John Watson]

Hi Mike, 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.

John