Author Topic: T4D #68 - RCD/GFCI  (Read 3814 times)

Monkeh

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T4D #68 - RCD/GFCI
« on: June 14, 2013, 11:49:32 AM »
If the toaster had a metal shell which could come in contact with a live conductor, it would be required to be earthed, as a Class I appliance. An RCD would absolutely guarantee a trip should such a fault occur, but would not be required for protection. A Class II (double insulated, non-earthed) appliance must be designed in such a way that a fault of that type cannot realistically occur. An RCD is not required for either case in normal installations. You are right, however, that an RCD would trip should you have a live, non-earthed metal case.

GFCIs work exactly the same way as RCDs, yes. They have a coil (current transformer) internally through which the line and neutral conductors are passed. Should there be a difference in current between them (current flowing back via another path, ie. either conductor contacting an earth path), the CT will register it (if the current is equal, it's cancelled out, and the CT registers no current). Once that imbalance reaches a sufficient level, the device operates. These devices are, except for minor differences in current level and reaction time, the same all around the world. No earth contact is required at the RCD itself, nor any device it protects.

I would suggest not feeding your entire bench from the RCD strip, and merely feeding devices you're working on and test circuits from one. Anything which is well made and intact does not require the protection, and having your entire bench go dark is pretty annoying.

classicmacintosh

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Re: T4D #68 - RCD/GFCI
« Reply #1 on: June 14, 2013, 01:11:50 PM »
With regards to the problem of US plugs being poorly designed:

What I would do is purchase and install some UK sockets (only in the lab) but wired up to the 110V mains supply, then attach UK plugs to your equipment - that way you won't have the problem of poor plug design and risk of being zapped!

Another (probably better) idea is to see if you can buy a few high-quality south african plug extension leads (or do they call them power boards, I can't remember) and install a high quality US plug.

Finally, you could ask BoomBoxDeluxe on YouTube [I am not affiliated with him], he has a (decidedly odd) obsession with mains plugs :) He would be able to point you in the right direction.

Sorry if it seems like I am trying to advertise a company here, but as I have no affiliation with them and have never used them before, it can't hurt.
Have a look here: http://www.stayonline.com/power-ac-plugs.aspx - they seem to sell all sorts of heavy duty and weird plugs.

(I do recognise this post is a complete mess, and not a good first impression to make, and I do apologise for this - English is my first language but I suck at getting my thoughts together! I blame Autism :) )

Ecobion

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Re: T4D #68 - RCD/GFCI
« Reply #2 on: June 14, 2013, 02:47:29 PM »
I posted something similar on the You Tube video. Martin could use a multiway socket adaptor for South Africa plugs, with a US mains lead. So long as whatever is being plugged in is 110V compatible, there shouldn't be a problem. I've actually done this the other way, we have a lot of family vising from Mexico, so I have a multiway 110V socket (4 of) wired up to a UK 240V mains plug. So long as their phone chargers, laptops, ipads, etc. have dual voltage, they don't need to worry about adaptors or step down transformers when staying in our house.

I've seen some multiway socket strips that feature sockets that take both UK and South African plugs with specially shaped holes for the plug pins.

There is one more way to join to cables, which I don't believe has been mentioned. Use an inline plug and socket, such as a telefunken (for 2 wire) or cloverleaf (3 wire) plug and socket, like they sometimes use on laptop PSUs.

SeanB

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Re: T4D #68 - RCD/GFCI
« Reply #3 on: June 14, 2013, 02:50:46 PM »
Actually it is very likely that there is a 220V 60Hz supply at the workbench for Martin to use, the common house wiring scheme in the USA is to have 2 phases to the house and have 110V between the phase and common and 230V between phases. This is for driers and aircons that are 220V units. Most sockets are often wired with 2 hot wires and a common wire, and an earth wire, or you can rewire to get the 220V to a socket and use the 220V US sockets, which have a similar shape but have the one power blade at a different orientation to the regular sockets.

SeanB

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Re: T4D #68 - RCD/GFCI
« Reply #4 on: June 14, 2013, 04:02:04 PM »
Look here for GFCI receptacles and inline units.

http://www.hubbellonline.com/040~Electrical_Systems/

A lot of good things there to upgrade the electricals.

Decent plugs and sockets.

http://www.hubbellonline.com/040~Electrical_Systems/020~Product_Information/.datasheet_pdfs/BSS104.pdf

GFCI for all uses

http://www.hubbellonline.com/040~Electrical_Systems/020~Product_Information/.datasheet_pdfs/H2626.pdf

http://www.hubbellonline.com/040~Electrical_Systems/020~Product_Information/.datasheet_pdfs/H5090.pdf


Hope this helps with safety on the lab. I like the Hubbell units, they are very strong and long lasting.

steve30

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Re: T4D #68 - RCD/GFCI
« Reply #5 on: June 14, 2013, 04:04:17 PM »
With regards to the problem of US plugs being poorly designed:

What I would do is purchase and install some UK sockets (only in the lab) but wired up to the 110V mains supply, then attach UK plugs to your equipment - that way you won't have the problem of poor plug design and risk of being zapped!


I was thinking of this earlier. English plugs are very well designed and made. I really don't get how the rest of the world manages without them  8).

That method would probably be best as a 'power strip' rather than permanently installed sockets, as they can be removed easily. Probably not likely, but it would help avoid the possibility that anyone else would think they are for 240V/50Hz.

SeanB

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Re: T4D #68 - RCD/GFCI
« Reply #6 on: June 15, 2013, 12:43:42 AM »
Martin did take his old lab with, complete with SA 16A socket outlets and plugs. Sure he has some extra plugtops there, or I will post him some if needed. That will work as above with no problem

MJLorton

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Re: T4D #68 - RCD/GFCI
« Reply #7 on: June 17, 2013, 04:38:40 PM »
Thanks to all of you for the input GFCI and ideas. I had also thought of using some of my SA power strips (in container...almost here) for the better plugs...but let me investigate some of the better US options first that have been sent my way.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

circuitous

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Re: T4D #68 - RCD/GFCI
« Reply #8 on: June 18, 2013, 09:53:09 AM »
With regard to the suggestion of having both live (we call them "hot" ) wires in one outlet box:
I'm not a certified master electrician (USA thing), but I have never seen two hot wires from separate circuits in one outlet box. 
I have seen two in some large light switch boxes, where two or three multi-way light switches are installed in one box.  I found that out after shutting off the breaker for the light I needed to work on then opened the box and checked that all of the lines were off.. surprise!... still a hot switched line fed from another switch.

My understanding is that there _should_ never be two hot wires in one box that are on separate circuit breakers.

I think that messing around with changing the plug style on mains power is iffy.  It's might be fine if you know what you're doing and you're the only one who might ever be in contact with that equipment, but it might surprise someone else.
Just my thoughts and safety concerns on the subject.