electrical testing of heating controls

[rustybits]

aya, what is the correct method of fully testing s and y plan heating controls after the fused spur etc. i understand the R1 +R2 back to the spur and also ZS from the furthest point but i struggle to understand how to carry out a "safe" insulation test without the possibilty of damaging valves, timers valves etc.
I have spoke to fellow sparks and we all have different ideas, your comments would be appreciated, r

 

[yellowvanman]

If you think the 500V insulation test could damage something then use the 250V setting on your tester.

 

[malcolmsanford]

If your doing either an initial verification or a PIR on the installation then the heating system including the boiler, its control circuits should be isolated as not to be part of the installation under testing. As you say you can damage them with the 500v IR test or get false reading via the components.

Most isolation of the boiler and control circuits is normally done by either switching of the system from a double pole FCU or un-pluging it from a BS 1363 socket.

If you talking about a domestic CH system then by the simple act of isolation as above will also isolate all over of the CH system. If there is a reason you can not disconnect the boiler, then you can carry out an IR test at 250volts between L/N joined to earth.

 

[rustybits]

thankyou for your reply. so if i were to test a new domestic heating circuit, after the inspection etc i would carry out r1 + r2, insulation (250v) and zs reading based on max earth fault loop impedance of the 5 amp bs1361 fuse in fcu, and then finally a rcd test, just like when we test any other "radial" circuit.

 

[malcolmsanford]

thankyou for your reply. so if i were to test a new domestic heating circuit, after the inspection etc i would carry out r1 + r2, insulation (250v) and zs reading based on max earth fault loop impedance of the 5 amp bs1361 fuse in fcu, and then finally a rcd test, just like when we test any other "radial" circuit.

The Zs reading is of the cable going to the supply side of the FCU and therefore you will use the corresponding value of Zs for the protection device of the circuit which if its an RCD will be 1667.

The 5 amp fuse on the load side of the FCU is to protect, most likely on a boiler, the flexible cable of that boiler, and so you dont need to include anything for that.

 

[rustybits]

again thankyou, i find this interesting. if i were to take a lighting circuit off of a rcd protected 32 amp ring main via a fcu rated at 5amp , are we saying the maximum ef loop impedance cannot be above 1.15 ohms (60898 32 amp mcb). i thought the max impedance would be based on the bs1361 5 amp fuse in the fcu, (8 ohm approx), r