more odd voltages in my boat

[simonfraser]

started to wire up the x over battery switch today
allows the house battery to start the OB and OB battery to power the fridge etc
so i have two main switches, for house and OB
add a x over from one switched live to the other switched live

all totally obvious as far as wiring was concerned, but i thought lets just make absolutely sure the positives are both at the same level
there is a working charger connected and a VSR so they should be the same right ?

checking the voltage of the live side of the switch and the common neutral on the bus bar, both bats 13.8 so that ok

now i am checking the voltage difference between positive house and positive OB, this showed as 13.8 EH ??
made no sense to me, should have shown zero or v low voltage difference surely ?
did not want to blow my meter so stripped some thin wire and touched the two positives, nothing no sparks etc
put the meter in series with the two positives, 0.15 A stable, no evidence if it 'settling'
(yes i know you'd not normally have both switches on AND the x over on)

wired the x over up with proper cables, nothing 'interesting' happenend, and yes can now start the OB with the house battery etc.

why did i have a 13.8 V difference between the two positives

 

[bobgarrett]

Because one of the positives was not on, so was actually at ground pulled down by units connected to it? When you connected the two positives together you just powered all those items.

 

[simonfraser]

Because one of the positives was not on, so was actually at ground pulled down by units connected to it? When you connected the two positives together you just powered all those items.

both on, both showed 13.8 live to -ve bus bar

 

[Mr Googler]

VSR is closed at 13.8 volts so batts joined anyway

 

[BruceK]

All I can say is leccy is lazy. It will take a path of least resistance when it has a choice and give unexpected results. Be like Mr G. When in doubt do the tongue test.

 

[John100156]

I thought you only used that test on 3 Phase supplies......

 

[BruceK]

@Mr Googler will lick anything, including the windscreen and windows.

 

[Mr Googler]

@Mr Googler will lick anything, including the windscreen and windows.

You’re an odd little man

 

[QBhoy]

Is this a split charge system with a relay ? That might explain it