2007 Track circuit calculation, Q3

[greensky52]

Thanks, Peter~But how do you know the addition relay is parallel with the 1st relay, but not in series with the 1st relay?

I think 840mA in your answer is wrong.... How does it come from?
It should be 1082mA-121mA=962mA, but not 840mA, right?
Please comment if I am wrong...

There are two relays - the question is about fitting a feed end relay of an identical type. As PJW notes

Then since we know that 121mA is going via the relay end relay and a further 121mA via the identical feed end relay, this leaves an absolute maximum of 840mA that can go into the ballast before the track is operating too close to bare minimum energisation to be considered reliably energised.

hence the total current is 1082mA, this is used up by two relays (at 121mA each) leaving 1082-(2 x 121) = 840mA as the max that can be soaked up by the ballast.