Post by JohnV on Nov 7, 2016 13:20:47 GMT
Recently I have come across posts stating that when there is an RCD on the boat and an RCD on the bollard that a fault on the cable between them will result in both RCD's tripping.
This must be wrong.
An RCD is a device that compares the current flow between the phase and the neutral.
If the currents match within the design specification the device does not trip.
Whatever the faults are that might occur upstream of the device, this does not and can not alter the balance of the current flow in the RCD.
The only occasions I have ever come across where an upstream fault has had any effect on downstream devices have been special situations.
Once it was an RCD on a rotating device that was combined with a voltage fail device.
The other was with one of the older generation of RCD's which were sensitive to asymmetric spikes, it was spotting ringing from large suppression devices on the protected circuit and was seeing these as fault currents. but not the upstream fault directly.
Investigation and the temporary removal of the suppressors proved this, replacement of the RCD with a different type solved it.
Reading other posts elsewhere seems to indicate that another common lack of understanding is in the differentiation required to prevent upstream devices being tripped by downstream devices.
I look forward to the feedback from other members.
This must be wrong.
An RCD is a device that compares the current flow between the phase and the neutral.
If the currents match within the design specification the device does not trip.
Whatever the faults are that might occur upstream of the device, this does not and can not alter the balance of the current flow in the RCD.
The only occasions I have ever come across where an upstream fault has had any effect on downstream devices have been special situations.
Once it was an RCD on a rotating device that was combined with a voltage fail device.
The other was with one of the older generation of RCD's which were sensitive to asymmetric spikes, it was spotting ringing from large suppression devices on the protected circuit and was seeing these as fault currents. but not the upstream fault directly.
Investigation and the temporary removal of the suppressors proved this, replacement of the RCD with a different type solved it.
Reading other posts elsewhere seems to indicate that another common lack of understanding is in the differentiation required to prevent upstream devices being tripped by downstream devices.
I look forward to the feedback from other members.
