ungrouned system

kimrichi

Member
if we have ungrounded system and a ground fault occures (line to line or line to case)does circuit breaker open is it a risk to touch the case
 

ActionDave

Moderator
Staff member
Line to line will trip a breaker. Line to ground (case) will not trip a breaker on the first fault, it establishes one phase as ground potential.

There should not be a shock hazard but the fault should be cleared as soon as possible which is why ground fault detectors are required.
 

G._S._Ohm

Senior Member
is it a risk to touch the case
Your body has capacitance to ground so there will be a tiny current to ground with 120vac. You probably will not notice it.
If you can find this capacitance value on the Web this current can be calculated.

An ungrounded helicopter connecting to a HV line has several mA flowing in the connecting jumper. The helicopter capacitance to ground is very low but the voltage is very high, and I = V/Xc, with Xc being the capacitive reactance.
 

jeremysterling

Senior Member
Naval shipboard electrical systems are ungrounded for battle readiness. The first ground fault will establish a ground reference and reduce motor operating efficiencies. If one of the remaining two legs faults to ground, the OCPD will open.
 

G._S._Ohm

Senior Member
Naval shipboard electrical systems are ungrounded for battle readiness. The first ground fault will establish a ground reference and reduce motor operating efficiencies. If one of the remaining two legs faults to ground, the OCPD will open.
Can you confirm what I've heard? That in the whole history of the Navy one person got electrocuted from a voltage as low as 47v?
I don't know if this was 400Hz AC or DC.

A phone line can deliver 56 vdc but it can't supply much current.
 
Top