Two pump wiring?

[Useroftheforce]

I need to build a low loss header – the primary circuit is 22mm and I have a spare 15/50 to power the new (shorter) primary circuit.
My question is about the wiring of the secondary pump into the Y plan distribution board.

I want to check out that it’s acceptable to wire the 15/50 pump in parallel with the existing 15/60 on the system circulation side of the low loss header.

Total 120w = 2amps. It's a 3 amp fuse in the heating circuit.

 

[stem]

I assume that you are going to wire the pumps together, so that they operate simultaneously.

The 2A load shouldn't be a problem. 3A fuses are designed to take 3A continuously without deterioration, it depends what the rest of the system takes. So you need to add it all up.

I would be concerned about what is switching on the pumps. If your boiler controls the pump, there will be a small relay mounted on the boiler PCB, if not, either the cylinder thermostat, or a microswitch in the motorised valve will switch it on. Because of having two pumps connected together the starting current and associated 'arcing' across the contacts may wear these components out fairly quickly.

You can get around this by fitting a more substantial relay that is switched by the present pump supply, The larger relay then switches the two pumps on. You could always connect the supply for the pumps to a separate 3A FCU, if you find that you will be taking too much from the boilers 3A FCU (The new FCU must be switched by the same isolator as the rest of the system though so you don't electrocute any service engineers or future occupants)

 

[Useroftheforce]

Brilliant - thanks alot.

 

[Biggles..]

normally the load side of the circuit(15-60) would be controleed by the y plan layout(stats and valve) plus timeclock,the shunt(15-50) would be powered by the timeclock and controlled by boiler stat and pipe stat.

relays are another way of doing the same thing.

your trying to acheive that the boiler doesnt always have to fire when the load side is running therefore creating better %eff.

its the starting current of the pumps that will cause the problems not the running therefore you could always uprate to a 5A as long as the cables are sized right.(remember boiler will have its own internal fuse for surge protection.)

Lee

 

[mikely]

120W = 0.5A, not 2A.

 

[stem]

120W = 0.5A, not 2A.

So it does, missed that. methinks 'Useroftheforce' thought W=V/A (120W=240V/2A) instead of W=VxA (120W=240V x 0.5A)

Okay, I know it's AC not DC and that it's 230ish volts these days.

 

[D_Hailsham]

Knowing that you have an Apollo, the primary pump must be wired into the boiler so the pump overrun thermostat can control the pump. The secondary pump should be fed from the switched live to the boiler, it then only comes on when the room and/or cylinder stat tells the boiler to run.

 

[Useroftheforce]

Thanks guys - it does exactly what it's supposed to - I just wired into the pump live from the boiler, so the shunt runs at the same time as the system pump. Since they are different size pumps and the bigger one runs the shunt, it works a treat.

It was definately worth all the calculations of which there are three pages and many many hours worth in excel. See my other recent post on this topic. Now I have the entire system sorted out properly I have to say the maths is pretty damn accurate.

Thanks in no small part to D_hailsham for sticking with my mathematical ineptitude.

Oh and David - having re-calculated the resistance on the new primary, I was wrong about the resistance of the magnaclean. The circuit itself is 3m at 0.4l/s. Since the 9 degree drop is present - it's checks out too.