economy 7 horstmann E7 tripping

8 Dec 2005
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United Kingdom
got a new twin immersion unvented direct cylinder and customer wants to use economy 7 for heating through the night on the bottom immersion and another circuit for boost as needed on the top immersion. got a horstmann electronic 7 programmer and connected up but it keeps tripping the rcd when the boost switch fused spur is turned on. the E7 and the normal heating circuit come from 2 seperate CU's and are both on rcds and then go to their own switch fused spurs and then into into the horstmann 7. the lives from the fused spur both go into one terminal on the horstmann and it seems that its sending current down the switched off economy 7 circuit and tripping. the manual says that it is compatible with economy 7 but not sure how this setup would work? any ideas?

cheers Si
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. the lives from the fused spur both go into ne terminal on the horstmann

Do you mean you have connected the Live from the fused spur fed by the economy 7 supply to the same contact in the timer as a Live supply from the fused spur fed by the normal permanent supply ?

Just be glad the RCD tripped out. That link you put in would have carried all the current required by the economy 7 equipment. If you have any storage heaters then they would have been permanently supplied via that link.

That could create a hazard and large electricity bills

If youhave a dual rate meter for the econony 7 then you only need the permanent Live feed to the timer. All the power used from the permanent supply will during the economy 7 periods be charged at the low rate.

Only if you have two separate meters would you need to make special provision ( two controllers ) for the two immersion heaters.
yea bernard both lives are wired in the same terminal in the programmer. the economy 7 is seperate from the the other immersion circuit. so the only way is to use 2 programmers then?

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You need a compatible unit, which electrically isolates the night and day supplies, so that the boost can be used independently of the night time circuit, so that current from one circuit does not backfeed into the other, causing possible danger, and RCD to trip out.

ALternatively just have the timer controller on the bottom night time circuit, and just use the 13amp DP fused spur switch to control the top booster element, as was the case on my old home.
The impression I get from the OP is that the lower immersion is fed from the E7 CU so will be controlled by the electricity supplier's timeswitch anyway as the storage heaters will be). The upper heater is for topping up during the day and fed from the on-peak CU

So there is no real need for a controller if this is the case

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