there is a DB board fed from a centre tapped transformer only on single pole breakers. The board feeds instrumentation. Is there any issue changing it to 110v and tie the neutral to earth there is no socket outlets fed on this so can’t see it as an issue?
As the voltage rises the chance of surviving a shock fall, so the exposure time has to be reduced - so we need the fault current to rise and the fault duration to fall.
That's a good point - 110V isn't RLV (unlike 50-0-50) so 5s disconnection times don't generally apply - table 41.1 seems to suggest 0.8s would be needed on TN systems (for final circuit <=32A and socket circuits <=63A). As it happens that'll likely be same same Zs as calculated above for most MCBs, but won't be for fuses (or possibly D-type MCBs).
As the voltage rises the chance of surviving a shock fall, so the exposure time has to be reduced - so we need the fault current to rise and the fault duration to fall.
That's a good point - 110V isn't RLV (unlike 50-0-50) so 5s disconnection times don't generally apply - table 41.1 seems to suggest 0.8s would be needed on TN systems (for final circuit <=32A and socket circuits <=63A). As it happens that'll likely be same same Zs as calculated above for most MCBs, but won't be for fuses (or possibly D-type MCBs).
