Low Voltage

[tony8404]

I am about to start a class in low voltage, was not presented with more info then low voltage. I have done a couple searches on low voltage, ac/dc low voltage but nothing comes up as like a tutorial or intoduction to low voltage. just wondering if i am missing something more then low voltage is there more to it in the name? i found a site called all about electronics and they have tutorials on alot of electronic stuff but nothing on low voltage just wondering if anyone knows of a good site to read on it or get familiar with it before i start my class next week... with the long weekend i wanted to read a little on it. thanks

 

[Willbe]

is there more to it in the name?

https://en.wikipedia.org/wiki/Extra-low_voltage
The 99' NEC seems to define "safe" as less than 30 v RMS, 42 v peak, 60 vdc.
There is also "dry circuit switching" but I can't imagine a whole class on this.

 

[tony8404]

that is where i am confused. my last instructor told us that the electronic system technicians would be going to low voltage. and the electrical construction maintenance would go to a pipe bending constructions class. i am lost

 

[crutschow]

Sounds like it refers to low voltage building wiring codes and techniques, i.e. control lines, sensor lines, signal lines, communication lines, alarm lines, etc.

 

[rjvh]

low voltage is normaly considered everythingh below 48 Volt

which is industrial controll circuits (24 volt) telephone circuits (48 volt)
The majority of alternative energy circuits ( lower than 48 volt)

Robert-Jan

 

[Diver300]

https://www.opsi.gov.uk/si/si1989/Uksi_19890728_en_1.htm#mdiv4

https://en.wikipedia.org/wiki/Low_voltage

According to those, "Low Voltage" is anything above 50 V and below 1000 V. It means standard supply voltages for homes and industry, single and three phase. "High voltage" is what is normally used to distribute electricity.

What is low and high depends on what you are comparing it with.

 

[crutschow]

https://www.opsi.gov.uk/si/si1989/Uksi_19890728_en_1.htm#mdiv4

https://en.wikipedia.org/wiki/Low_voltage

According to those, "Low Voltage" is anything above 50 V and below 1000 V. It means standard supply voltages for homes and industry, single and three phase. "High voltage" is what is normally used to distribute electricity.

What is low and high depends on what you are comparing it with.

So what do you call voltages below 50V?

 

[Hero999]

Extra Low Voltage (ELV) which is defined as below 50VAC or 120VDC which is still considered a shock hazard just not a severe shock hazard.

The stadards for what is safe vary by country and the environment where the circuit is concerned. For example, here in the UK the upper limits for exposed conductors in a dry area are 25VAC or 60VDC but in a wet area this is reduced to just 12AC or 30VDC.

Any appliance operated from ELV doesn't require to have an safety earth conductor.

Here in the UK we also have reduced voltage which is 110VAC, as in the US, but the difference is that the voltage between each line and earth should be under 63.5VAC. This is because it can be supplied by a centre tapped transformer (55-0-55V which is normally the case) or a three phase star transformer giving 63.5VAC per phase to neutral.

Reduced voltage is normally used on building sites and other areas where cables could be easilly cut.

 

[architmh]

below 50 V is ELV....but it depends on wat u r comparing it with....but a whole class on LV....wat will it actually be all abut..

 

[Willbe]

as below 50VAC or 120VDC which is still considered a shock hazard just not a severe shock hazard.

in a wet area this is reduced to just 12AC or 30VDC.

50 vdc from the phone landline is barely detectible to me with dry skin so I'd say ~1 mA is flowing.

I have heard that the sewer workers in the U.S., standing in water, have lights powered by 28 v so from your post I'd guess it is 28 vdc and not ac.

 

[Hero999]

Are you agreeing or disagreeing with me?

Your post backs up what I've said.

AC is considered to be more dangerous, for example with dry skin you won't be able to feel 50VDC but 50VAC will probably give you quite a shock.

 

[Willbe]

Are you agreeing or disagreeing with me?

Yes!

 

[Hero999]

I wonder why the maximum safe AC voltage is 30VAC in the US and only 25VAC in the UK. I think this is probably because 50Hz is considered to be more dangerous than 60Hz.

 

[Nigel Goodwin]

I wonder why the maximum safe AC voltage is 30VAC in the US and only 25VAC in the UK. I think this is probably because 50Hz is considered to be more dangerous than 60Hz.

I think they are both just figures invented by a committee and are both drastically lower than actually required. A voltage been dangerous or not varies wildly according to many criteria, not the least of which is the individual concerned.

I would also suggest the committees both just halved the mains frequency and used that number!

 

[Leftyretro]

Low voltage is not a very specific term and it needs to be referenced to some standard or context to be a useful term. I also considered low voltage to be anything up to 24 volts. I was in for a shock (that's a pun ) when I went to work at a refinery. While I was working instrumentation, I was around a lot of the electricians that worked there. They used the NEC standards where anything up to 480V was considered low voltage, 480 to 2.4kv as medium voltage (I think) and above that (we had mostly 12kv main feeders) considered high voltage. So the industry and standards really give context to rating definitions.

Me, I'll stick with 24v and down, with only sometimes a tip toe into 120vac world. I used to repair CRTs several decades ago and they would sometimes zap me even when turned off. Had to learn how to discharge the damn anode clip

Lefty

 

[Hero999]

Generally low voltage just means it's too low to arc from one terminal to another and from that point of view it's considered to be failrly safe.

Shock hazard is a different issue altogether and depends on many factors but the risk of the person comming into contact with the voltage and the how wet the environment is are normally included in most standards.