Safety question
- Thread starter Rob Flinn
- Start date
Help Support GroupDIY Audio Forum:
> rather than a Ground leakage type ?
I am 99% sure that RCB and GFI work the *same*. They detect the difference between the two intended current conductors.
There are different numbers. But the number of mA is a short-hand for a time versus current curve. I am curious if the numbers are measured at different times, and really on the same curve.
When National Semi tried to market a GFI chip (LM1851), they explained an R-C network on it. The value of R set the long-term trip current. The value of C set the curve of the higher short-term current trip. Obviously this R-C could be tailored to suit different national regulations. And the US NatSemi GFI part could have been used in UK RCBs with appropriate R-C. (In fact the UK electric industry would favor a UK-sourced part, and apparently the US industry felt likewise; the NS GFI part was only in the book for a year or so.)
That said... the differences in plugs and wire-colors do suggest using US/Can devices on 115V power.
Newer GFIs have LED indicators. If RCBs do too, they may work poorly on half their intended voltage. In fact the trip-out coil may just fail to TRIP with a supply voltage far below the design voltage.
________________________________
US "neutral", the CT of the 240V, is, as said, tied to dirt at the Service Entrance of the house. Further the street line low-lead is tied to dirt every 1 to 4 poles (not a lot of underground service here). All of this is "needed" to divert lightning strikes in a least-dangerous way. The "ground" inside really has other purposes (unless lightning comes inside the house!). While it nominally puts your washing machine case at a potential similar to the concrete it stands on, the inside grounding is really so when the 120V live wire inside the machine pops-off and touches the case, the circuit fuse will blow and render the machine safely dead. Use of power ground to damp the buzz in your guitar amp is not really considered in Code. As you see, JR is not required to have a quiet-grounded guitar-amp outlet in his bathroom(!), though he is encouraged to use a GFI so when he plays in the tub he is less likely to die.
________________________________
> specialty line cord plugs that sense for current in the ground
That won't cover the case of a frayed cord, or finger inside the case, with user standing on dirt. The leakage may not flow through line cord, but rather through dirt (concrete, sink faucet, heating pipes....).
Sub-Amp cord ground leakage would seem to be aimed at equipment protection? Or the special needs of heart surgeries, where "any" leakage would be cause to remove that gizmo from the operating room before it got near an open heart.
I am 99% sure that RCB and GFI work the *same*. They detect the difference between the two intended current conductors.
There are different numbers. But the number of mA is a short-hand for a time versus current curve. I am curious if the numbers are measured at different times, and really on the same curve.
When National Semi tried to market a GFI chip (LM1851), they explained an R-C network on it. The value of R set the long-term trip current. The value of C set the curve of the higher short-term current trip. Obviously this R-C could be tailored to suit different national regulations. And the US NatSemi GFI part could have been used in UK RCBs with appropriate R-C. (In fact the UK electric industry would favor a UK-sourced part, and apparently the US industry felt likewise; the NS GFI part was only in the book for a year or so.)
That said... the differences in plugs and wire-colors do suggest using US/Can devices on 115V power.
Newer GFIs have LED indicators. If RCBs do too, they may work poorly on half their intended voltage. In fact the trip-out coil may just fail to TRIP with a supply voltage far below the design voltage.
________________________________
US "neutral", the CT of the 240V, is, as said, tied to dirt at the Service Entrance of the house. Further the street line low-lead is tied to dirt every 1 to 4 poles (not a lot of underground service here). All of this is "needed" to divert lightning strikes in a least-dangerous way. The "ground" inside really has other purposes (unless lightning comes inside the house!). While it nominally puts your washing machine case at a potential similar to the concrete it stands on, the inside grounding is really so when the 120V live wire inside the machine pops-off and touches the case, the circuit fuse will blow and render the machine safely dead. Use of power ground to damp the buzz in your guitar amp is not really considered in Code. As you see, JR is not required to have a quiet-grounded guitar-amp outlet in his bathroom(!), though he is encouraged to use a GFI so when he plays in the tub he is less likely to die.
________________________________
> specialty line cord plugs that sense for current in the ground
That won't cover the case of a frayed cord, or finger inside the case, with user standing on dirt. The leakage may not flow through line cord, but rather through dirt (concrete, sink faucet, heating pipes....).
Sub-Amp cord ground leakage would seem to be aimed at equipment protection? Or the special needs of heart surgeries, where "any" leakage would be cause to remove that gizmo from the operating room before it got near an open heart.
The GFCI chip sets have some RC lag engineered in to prevent nuisance trips from inductive spikes, or other line noise.PRR said:
JR
I thought there were 2 types of breaker the ELCB (Earth leakage Contact breaker), which trips when it registers a current going down the Earth cable.
"An Earth-leakage circuit breaker (ELCB) is a safety device used in electrical installations with high Earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected."
Then secondly the RCD (residual current device) which trips when it detects an imbalance on live & neutral. I could be wrong here because I don't hold sparky qualification, but I think in the UK we used to use the ELCB type but they were superceded for new installations by the RCD.
This article seems to cover most types of breaker
http://electrical-engineering-portal.com/what-is-the-difference-between-mcb-mccb-elcb-and-rccb
"An Earth-leakage circuit breaker (ELCB) is a safety device used in electrical installations with high Earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected."
Then secondly the RCD (residual current device) which trips when it detects an imbalance on live & neutral. I could be wrong here because I don't hold sparky qualification, but I think in the UK we used to use the ELCB type but they were superceded for new installations by the RCD.
This article seems to cover most types of breaker
http://electrical-engineering-portal.com/what-is-the-difference-between-mcb-mccb-elcb-and-rccb
> 2 types of breaker
> the ELCB
> the RCD
OK.
I think that page is lightweight, but let's see what it says:
> ELCB (Earth Leakage Circuit Breaker)
> Phase (line), Neutral and Earth wire connected through ELCB.
> RCCB - Residual Current Circuit Breaker
> Phase (line) and Neutral both wires connected through RCD.
Our GFI is same-as your RCCB ("RCB,RCD"). Line and Neutral go *through*. Ground does not.
We have GFI outlets. It may appear that ground goes through (ground current could be sensed). In fact it does not. I have autopsied these things. The incoming ground screw is on a frame which holds the contacts for the 3rd pin holes. Connect but not sense. As further evidence: our GFI outlets have added Hot and Neutral OUTputs, for adding GFI-protected plain outlets "downstream", but no added feed for ground (we wirenut all the greens together).
We also have GFI which go in the fusebox, combination 20A over-current and shock-protect. Here it is clear that Neutral goes *through* (messing-up our neutral bus convention) and ground doesn't go near the GFI, goes-around.
http://www.do-it-yourself-help.com/images/gfci-circuit-breaker-wiring.gif
Looking at this-- know that in a US main breaker box, the breakers snap onto a heavy (200A!) "bus". The snap is roughly behind the "20A" marking in this image. That's how "hot" gets in. A plain over-current breaker has one hot output screw.
The GFI breaker has a white (neutral) pigtail run to the neutral bus, and a second output screw where you land the white wire from the load. Note that green bypasses the GFI.
Also FYI: in basic US home fuseboxes, Ground and Neutral are most commonly the same bus. This is our "single N-G connection". In most cases the utility company does not supply a dedicated ground from the street, N and G are the same wire. However where additional fuseboxes are fed from a Entrance fusebox, we are supposed to segregate N and G. They sell add-on insulated Neutral buses for the purpose. I have wired my new cellar box this way. Since I added a new fusebox at my meter-pole, the cellar box is now a sub-panel. In fact I am living in sin because I do not have a dedicated ground conductor from pole to cellar. However I could change that (it has backhoe damage) so I am ready. Meanwhile I have white and green buses, and a clearly marked jumper tie.
> the ELCB
> the RCD
OK.
I think that page is lightweight, but let's see what it says:
> ELCB (Earth Leakage Circuit Breaker)
> Phase (line), Neutral and Earth wire connected through ELCB.
> RCCB - Residual Current Circuit Breaker
> Phase (line) and Neutral both wires connected through RCD.
Our GFI is same-as your RCCB ("RCB,RCD"). Line and Neutral go *through*. Ground does not.
We have GFI outlets. It may appear that ground goes through (ground current could be sensed). In fact it does not. I have autopsied these things. The incoming ground screw is on a frame which holds the contacts for the 3rd pin holes. Connect but not sense. As further evidence: our GFI outlets have added Hot and Neutral OUTputs, for adding GFI-protected plain outlets "downstream", but no added feed for ground (we wirenut all the greens together).
We also have GFI which go in the fusebox, combination 20A over-current and shock-protect. Here it is clear that Neutral goes *through* (messing-up our neutral bus convention) and ground doesn't go near the GFI, goes-around.
http://www.do-it-yourself-help.com/images/gfci-circuit-breaker-wiring.gif
Looking at this-- know that in a US main breaker box, the breakers snap onto a heavy (200A!) "bus". The snap is roughly behind the "20A" marking in this image. That's how "hot" gets in. A plain over-current breaker has one hot output screw.
The GFI breaker has a white (neutral) pigtail run to the neutral bus, and a second output screw where you land the white wire from the load. Note that green bypasses the GFI.
Also FYI: in basic US home fuseboxes, Ground and Neutral are most commonly the same bus. This is our "single N-G connection". In most cases the utility company does not supply a dedicated ground from the street, N and G are the same wire. However where additional fuseboxes are fed from a Entrance fusebox, we are supposed to segregate N and G. They sell add-on insulated Neutral buses for the purpose. I have wired my new cellar box this way. Since I added a new fusebox at my meter-pole, the cellar box is now a sub-panel. In fact I am living in sin because I do not have a dedicated ground conductor from pole to cellar. However I could change that (it has backhoe damage) so I am ready. Meanwhile I have white and green buses, and a clearly marked jumper tie.
Inneresting essay on the two different names:
http://www.electronicspoint.com/threads/gfci-and-rcd.166596/
We are divided by our common language.
More than you want to know about the deep history of such devices:
http://definedelectric.com/safety-security-residual-current-device/
Mike Holt's forum is generally very-expert, though totally US-centric:
http://forums.mikeholt.com/showthread.php?t=122329
Unusually they have someone from London (UK!) in the thread.
http://www.electronicspoint.com/threads/gfci-and-rcd.166596/
We are divided by our common language.
More than you want to know about the deep history of such devices:
http://definedelectric.com/safety-security-residual-current-device/
Mike Holt's forum is generally very-expert, though totally US-centric:
http://forums.mikeholt.com/showthread.php?t=122329
Unusually they have someone from London (UK!) in the thread.
Similar threads
