3 ms·

> If you think the National Electrical Code means that your circuit breakers will safely and reliably trip in the event of a fault, e.g. a neutral-to-ground sho

> If you think the National Electrical Code means that your circuit breakers will safely and reliably trip in the event of a fault, e.g. a neutral-to-ground short or a cut, stripped live wire stuck directly into wet Earth, I have some snake oil to sell you. Could you expand on this a bit? Do you mean that ground fault interrupters are not fast enough/threshold currents too high to prevent harm in some cases? (Non American; not familiar with your National Code but curious)

bombcar 3y ago
Even the best arc fault breakers (which are NOT the same as ground fault breakers) will not detect certain faults, mainly those that look like normal usage. A GFCI should detect a live wire into wet ground IF a ground is present, but not all breakers are required to be GFCI.
jsjohnst 3y ago
> Do you mean that ground fault interrupters are not fast enough/threshold currents too high to prevent harm in some cases? There’s some over generalization and outright misinformation in this thread. The required threshold for a Type A GFCI (aka normal residential) is 6mA in the US. GFCI breakers or outlets just need “another path” for the electricity to flow to trigger. Water / grounding / etc are not required, it could be a largish capacitor recharging. The way GFCIs work is by detecting a current imbalance between the positive and neutral wires. Electricity flows in a loop, so if more current is going out on the positive wire than what’s returning on the neutral wire, then it has to be going somewhere which could be bad if say it’s a hairdryer in the bathtub, but very much might be fine in the case of a VFD used with a spindle on a hobby CNC.
amluto 3y ago
GFCIs are great: they detect even small leakage currents and modern ones also detect neutral-to-ground faults. But, in the US, it’s very unusual to have any sort of ground fault/residual current protection on anything other than individual branch circuits, and even then it’s usually just the outlets. GFCIs are also fixed at 5mA, and they don’t coordinate with each other (meaning that if you have two GFCIs in series, they are both likely to trip in the event of a fault). So individual outdoor wires in rust metallic conduit without GFCI protection are very common. Outdoor receptacles in nice “extra-duty” boxes, where the receptacle itself has “weather resistant” GFCI (modern code) are very common, and nothing protects effectively against water getting into the box itself and causing a problem immediately upstream of that fancy GFCI. I don’t understand the European codes well, but as I understand it, it’s common to have a big RCD in the distribution box, and that will protect the distributed wiring even if it doesn’t have the magical 5mA threshold that supposedly makes wires extra safe if you touch them by accident. (I’d like to see standardized ratios of ground fault current sensitivity to breaker size, so a 15A residual current device downstream of a 60A one would coordinate properly. The hardware is cheap enough these days that this could be done cost-effectively.

bombcar 3y ago

Even the best arc fault breakers (which are NOT the same as ground fault breakers) will not detect certain faults, mainly those that look like normal usage. A GFCI should detect a live wire into wet ground IF a ground is present, but not all breakers are required to be GFCI.

jsjohnst 3y ago

> Do you mean that ground fault interrupters are not fast enough/threshold currents too high to prevent harm in some cases? There’s some over generalization and outright misinformation in this thread. The required threshold for a Type A GFCI (aka normal residential) is 6mA in the US. GFCI breakers or outlets just need “another path” for the electricity to flow to trigger. Water / grounding / etc are not required, it could be a largish capacitor recharging. The way GFCIs work is by detecting a current imbalance between the positive and neutral wires. Electricity flows in a loop, so if more current is going out on the positive wire than what’s returning on the neutral wire, then it has to be going somewhere which could be bad if say it’s a hairdryer in the bathtub, but very much might be fine in the case of a VFD used with a spindle on a hobby CNC.

amluto 3y ago

GFCIs are great: they detect even small leakage currents and modern ones also detect neutral-to-ground faults. But, in the US, it’s very unusual to have any sort of ground fault/residual current protection on anything other than individual branch circuits, and even then it’s usually just the outlets. GFCIs are also fixed at 5mA, and they don’t coordinate with each other (meaning that if you have two GFCIs in series, they are both likely to trip in the event of a fault). So individual outdoor wires in rust metallic conduit without GFCI protection are very common. Outdoor receptacles in nice “extra-duty” boxes, where the receptacle itself has “weather resistant” GFCI (modern code) are very common, and nothing protects effectively against water getting into the box itself and causing a problem immediately upstream of that fancy GFCI. I don’t understand the European codes well, but as I understand it, it’s common to have a big RCD in the distribution box, and that will protect the distributed wiring even if it doesn’t have the magical 5mA threshold that supposedly makes wires extra safe if you touch them by accident. (I’d like to see standardized ratios of ground fault current sensitivity to breaker size, so a 15A residual current device downstream of a 60A one would coordinate properly. The hardware is cheap enough these days that this could be done cost-effectively.