Gfci for 24 V

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Dennis Alwon

Dennis Alwon

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Does anyone know if there is gfci for a 24v circuit? I can't see how this would work but I know someone who is installing 24 v heaters in shower heads at a hospital and they would feel better with gfci protection.

My feeling is even if a wire should break loose and energize the head there really is no path back to the source so it would seem safe. The manufacturer does not appear to require it either.

First - do they make a 24v gfci
Secondly - discuss the safety
 
Dennis Alwon said:
Does anyone know if there is gfci for a 24v circuit? I can't see how this would work but I know someone who is installing 24 v heaters in shower heads at a hospital and they would feel better with gfci protection.

My feeling is even if a wire should break loose and energize the head there really is no path back to the source so it would seem safe. The manufacturer does not appear to require it either.

First - do they make a 24v gfci
Secondly - discuss the safety
Click to expand...

This sensor seems like it should work, as long as the 24V is AC and not DC.

https://www.automationdirect.com/ad..._Encoders/Ground_Fault_Sensors/GFS30-M1B-24-F



SceneryDriver
 
So I am trying to imagine how that works... There is no ground in the 24v circuit and if the conductor from the 24v side touches a shower head how would any current leak back to trip the gfci?
 
I'm not sure it's necessary IF it is a Class 2 circuit, but that then means limited to 100VA. Not much of a heater. I'd look at the requirements for swimming pool lights, similar in that the power is potentialy in direct contact with the humans if there is a problem.
 
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The first ground fault would not cause any fault current, it would just ground one conductor. Like you said, without a return path it wouldn't trip any GFDI devices. The problem would happen with the 2nd ground fault, which would create a parallel path or a short.

At higher DC voltages (i.e. a PV array), ground fault detection on an ungrounded system is typically done through isolation monitoring. I'm not too familiar with 24Vdc circuits and what products are available.

Dennis Alwon said:
Does anyone know if there is gfci for a 24v circuit? I can't see how this would work but I know someone who is installing 24 v heaters in shower heads at a hospital and they would feel better with gfci protection.

My feeling is even if a wire should break loose and energize the head there really is no path back to the source so it would seem safe. The manufacturer does not appear to require it either.

First - do they make a 24v gfci
Secondly - discuss the safety
Click to expand...
 
Dennis Alwon said:
So I am trying to imagine how that works... There is no ground in the 24v circuit and if the conductor from the 24v side touches a shower head how would any current leak back to trip the gfci?
Click to expand...

It would not work unless you make the 24 volt supply bonded to ground like any SDS.
 
Thanks all for the replies

Jraef said:
I'm not sure it's necessary IF it is a Class 2 circuit, but that then means limited to 100VA. Not much of a heater. I'd look at the requirements for swimming pool lights, similar in that the power is potentialy in direct contact with the humans if there is a problem.
Click to expand...

Yes but in a pool the transformers must be listed for pools-- not sure exactly what that entails..

iwire said:
It would not work unless you make the 24 volt supply bonded to ground like any SDS.
Click to expand...
Yes I thought of that also. I remember eating my teeth in a crawl space when I touched a 24v telephone line. I thought that was from touching one wire and being grounded but that doesn't make sense.
 
Since the phone line DC (and the 90V AC ringing voltage) are referenced to ground at the source, touching one wire and the earth can certainly complete a circuit through you.

mobile
 
Dennis Alwon said:
Does anyone know if there is gfci for a 24v circuit? I can't see how this would work but I know someone who is installing 24 v heaters in shower heads at a hospital and they would feel better with gfci protection.

My feeling is even if a wire should break loose and energize the head there really is no path back to the source so it would seem safe. The manufacturer does not appear to require it either.

First - do they make a 24v gfci
Secondly - discuss the safety
Click to expand...

Do you have a link to the product? Something seems off. The heater has to be like 500-1,000A at 24v to make enough hot water to shower on the fly and you can't carry 24v long distance at such power level so you're going to have a 200 lb transformer right behind the wall or above the ceilling.
 
GoldDigger said:
Since the phone line DC (and the 90V AC ringing voltage) are referenced to ground at the source, touching one wire and the earth can certainly complete a circuit through you.

mobile
Click to expand...

I figured it must be if my recollection was correct. Didn't realize the ringing voltage was 90V....
 
Electric-Light said:
Do you have a link to the product? Something seems off. The heater has to be like 500-1,000A at 24v to make enough hot water to shower on the fly and you can't carry 24v long distance at such power level so you're going to have a 200 lb transformer right behind the wall or above the ceilling.
Click to expand...


I don't have info on the equipment
 
GoldDigger said:
Since the phone line DC (and the 90V AC ringing voltage) are referenced to ground at the source, touching one wire and the earth can certainly complete a circuit through you.

mobile
Click to expand...

Yep, and CATV will do it now too. Always nice kneeling on damp ground when someone calls the landline you are working on.
 
I really think it was misread or the 0 was accidentally left out from 240v. Electric shower is in 10-20kw range depending on GPM and rise temp required. I don't see any safety advantage in using 24v. Taking a shower at hospital doesn't make you more vulnerable to shock. The heating unit (a tiny pressurized bucket with three times the heating power of regular full size water heaters) is obviously solidly grounded.

To have it be a shock hazard, I think it would have be installed quite negligently. I suppose it's possible for shower head to become electrified if you used PVC water supply line to the heater, all copper from heater to shower without any grounding and install the heater without grounding. With all that said. That's why you should have it behind a GFi
 
Electric-Light said:
I really think it was misread or the 0 was accidentally left out from 240v. Electric shower is in 10-20kw range depending on GPM and rise temp required.
Click to expand...

Well, I agree that 24v shower head doesn't make any sense, however, they are not 10-20kw. My sun was in Ecuador years ago and they had a shower head fed with a 12 or 10 gauge. He called me to say he gets a shock when he touched the shower head... I told him don't touch it.

I asked for the info on this unit--we'll see if I get it
 
If the unit is just giving the water some final tempering it may not need to be too high of wattage, if you are heating 55 degree water to ~105 degrees then yes you will be looking at a huge current at 24 volts, flow rate will be critical as well.
 
kwired said:
If the unit is just giving the water some final tempering it may not need to be too high of wattage, if you are heating 55 degree water to ~105 degrees then yes you will be looking at a huge current at 24 volts, flow rate will be critical as well.
Click to expand...


Good point.. I suspect that it is using the hot water in the building and boosting it a bit
 
The "electric showers" (scary name if you ask me) that I saw last time I was in Europe were between 8 and 10kW and were always 230V. They work surprisingly well actually, and as you might imagine, you never run out of hot water. They think the way we do it here is nuts! But that said, the idea of this piece of electrical equipment in your shower with you is frightening. You are essentially putting your life in the hands of the electrician that installed it, a little more than normal. You are also relying on the continuous integrity of the seal they put on the cover, all of the electrical components are right there in he shower with you, there is a big device looking like a giant sprinkler timer right under the shower head.

This gives you a good view of the insides, they are all very similar. I never installed one, but after seeing it in my Aunt's house, I went to the hardware store and looked at a couple.
http://www.explainthatstuff.com/electricshowers.html
 
Jraef said:
The "electric showers" (scary name if you ask me) that I saw last time I was in Europe were between 8 and 10kW and were always 230V
Click to expand...

It would be a big problem if they became popular in the US and completely throw off current calculations for load factor and probably aggravate the problems solar PVs are already causing. Our distribution system may not be able to handle substantially overlapping demand and would likely have to use 80-90% coincidence factor of electric showers due to 9-5 tradition.

I believe utilization voltage originates from a much larger network of transformers in Europe rather than the way it is done in the US neighborhoods.
 
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