| Shel-e-bean |
I have a Yamaha "Natural Sound" CT-610 tuner. It is an analog unit from the 70s. I was doing a cleanup on it when I noticed that there is a resistor (measures about 2.2 meg) going from a line voltage wire to the chassis. The power plug is non-polarized 2 wire, typical from that era. The power switch switches the transformer secondary... The transformer is always energized.
Being an Electrician (but not an electronics technician), I chopped off the cord cap and replaced it with a 2-wire polarized plug, making the wire with the resistor attached always plugged into the building neutral (which is always grounded).
My questions.. Why bother putting in this resistor at all?
Why switch the xfrmr secondary and not the primary?
The Yamaha engineers must have had a reason.. but what? Maybe because this was high end gear, it was more to do with niggly stuff. |
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| cpemma |
| So the 'resistor' is in parallel with the transformer primary? You sure it's an ordinary resistor and not a varistor for suppressing mains spikes? |
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| SY |
Back in the '70s, three wire plugs were not very common. Today they are and they're MUCH safer- and unless the tuner has a double-insulated case, they're required (as an electrician, you're probably more familiar with this than most).
I'd update it to current standards. That means three wire cord, green wire FIRMLY attached to chassis, and the transformer primary totally isolated from ground.
And keep the 2.2M in a box somewhere as a souvenir. BTW, what did it look like? It's possible that it was an MOV or something like that. |
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| Shel-e-bean |
Hi cpemma and SY.
Here is a pic. There are more pics, including inside shots of newer models at
http://audiokarma.org/forums/showthread.php?t=75738
I'm not sure if non-members can see the pics though...?
The newer models have a resistor and an mov (or a cap- I can't tell) connected to the chassis, the older "non II" models just have a resistor. I was worried that in a catastrophic situation, the chassis could become highly en-live-enated and en-jigglefy anyone that touches it. |
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| SY |
| That's an excellent worry. Three wire! Green one to the chassis with a star washer, well torqued down. Resistor chopped out and mashed to bits under repeated hammer blows. |
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| Shel-e-bean |
I'm not an electronics tech, so my worry with adding a ground wire would be ground loops. Not even new equipment has 3 wire cords... they just use standard polarized 2 wire cords like incandescant lamps. (In the old days, you could get a shock just changing a lamp's bulb if the screw shell was hot. You could plug it in any old way. There was no upside-down). I guess the new equipment is electrically isolated from the mains. To me, the wonderment comes from the fact that tuners aren't like tape players... They need antennas. That involves grounding. My head is spinning. javascript:smilie(':xeye:')
xeye |
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| mrshow4u |
| my understanding of that 2.2 MegOhm resistor is to supply a discharge path if the chassis voltage floats above the line voltage due to static buildup and what-not. If there is no other leakage path from your perhaps floating chassis, there is a danger that static electricity could arc through the varnish on your transformer windings. The 2.2 Meg resistor bleeds these currents off to the AC grid. If you decide to wear rubber shoes and comb your hair, then touch the volume knob your generated static will be bled through the resistor and not through a hole punctured in the transformer winding varnish. ...at least that is my understanding. |
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| SY |
New equipment with two wire power cords will be double insulated. Your chassis is not! Metal chasses will always be grounded and used with three wire cords.
Ground loops are a separate issue; the three wire system just provides a safety ground. Your signal ground can be tied to the chassis ground at one point. If ground loops develop, the signal ground can be lifted from the safety ground via a small (20 ohm) resistor to break up the loop. Do NOT lift the safety ground under any circumstances. |
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| mrshow4u |
| "...why switch the secondary and not the primary?". That's a quizzler. . I don't think it would have been a question of money. A difference in switch contact rating for current and flashover shouldn't be an issue. They were already switching the primary's on their receivers. Maybe they couldn't get in under the wire for UL or CSA certification?? Perhaps it reduced certification headache to just hardwire all of the line side and switch the isolated side? I think putting on the polarized plug with the resistor always on the neutral side is not a bad idea. You'll measure less chassis to earth voltage than you would get if the plug was flipped (assuming the resistor is the dominant leakage path). I don't think there would be any impact on any "ground loop" related issues, but your fingertips would know the difference if you were grounded and lightly touching the chassis. |
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| AndrewT |
Hi,
I am real glad I live in the UK.:cool: :devilr: |
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| cpemma |
| quote: | Originally posted by AndrewT
Hi,
I am real glad I live in the UK.:cool: :devilr: |
You surely remember our 2-pin sockets? :hot: :eek: |
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| AndrewT |
Hi,
my age must be playing tricks with my memory.
Did we have 2 pin sockets in the UK after WW2?
I can recall the 13A rect pin, 15A round pin, 5A round pin. But that's my limit. |
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| lndm |
| If I can vaguely remember a conversation I had many years ago, Britain may have introduced 3 pin sockets before Australia even had a mains supply (if I'm wrong, maybe at the least it was on the drawing board). |
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| Shel-e-bean |
| quote: | Originally posted by mrshow4u
"...why switch the secondary and not the primary?".
<snip>
I don't think there would be any impact on any "ground loop" related issues, but your fingertips would know the difference if you were grounded and lightly touching the chassis. |
I think it may have something to do with static as Mrshow4u said. There is a connector on the back for coax cable, the shield connects to chassis ground. I'm just imagining various situations with antennea from the 70s fluttering in the wind, pointing to lightning with it's come-hither little fingers
I didn't realize that a ground loop could be broken with a mere 20 ohm resistor.
There was a lightning storm here last night. The grounding system in this house sucks. I think I'll just sell the tuner on Craigslist.
PS- This is a pretty cool site. :-) |
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| cpemma |
| quote: | Originally posted by AndrewT
Did we have 2 pin sockets in the UK after WW2?
I can recall the 13A rect pin, 15A round pin, 5A round pin. But that's my limit. |
My parents' house was built immediately after the war and had some 2-pin 5A sockets mounted on the skirting board when we moved in, along with 15A 3-pin to run an electric fire. Not many, it was common practice then to run the hoover upstairs via a 2-pin to bayonet adaptor from a ceiling light fitting.
The 13A system came in in 1947 but I guess took a few years to reach Yorkshire, plus it involved running a ring main rather than just another spur or swapping the socket.
RS still stock the 5A & 15A 3-pins. |
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| AndrewT |
Hi Cpemma,
thanks for that link, I'll go back and read it properly.
Mullins talks about BS546, the predecessor to BS1363 flat pin plug & sockets.
BS546 seems to have been the standard upto and through WW2 but he makes no mention of 2pin sockets.
I wonder if the sockets, you mentioned, were old stock and all that was available due to the war effort?
Makes me wonder just how old those 2pin sockets were and what plugs were available to fit them?
Do not confuse a 2pole +earth system for 2pin. |
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| cpemma |
| quote: | Originally posted by AndrewT
Makes me wonder just how old those 2pin sockets were and what plugs were available to fit them? |
| quote: | From Wikipedia
5A 2 pin
This plug is what became the UK standard shaver plug and is similar but slightly larger than the Europlug. British shaver sockets and adaptors tend to be sized to accept this, Europlugs and two pin American and Australian plugs. |
I remember a plastic hemispherical body, the back screwed off, the flex went through a polar hole and was attached to the pins. Much like a current bulb holder. Pins were split to provide a better grip in the socket. |
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| lndm |
Now this has me curious. I found out that Australian, New Zealand, Papua New Guinea, sockets were standardised in 1937/38.
No one I know has ever seen a two pin socket. Does anyone here have any idea what we did before 1937? |
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| mrshow4u |
| Is this really true??? No 2-pin sockets?? I certify a lot of equipment from Korea and Japan and most if not all comes with two pin plugs. I guess I should say that current electrical code for receptacles/sockets here is 3-wire grounded or GFI for kitchens and bathrooms. Many older houses still have 2-pin receptacles. Many if not most consumer electronics come with 2-wire plugs, however. |
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| lndm |
| There are many appliances that use two pin plugs, its just the outlets, all 3-pin and switched. |
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| Shel-e-bean |
| Does the UK system use a "neutral"? IE, a main conductor bonded to ground (earth)? |
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| AndrewT |
Hi,
our "neutral" varies depending on which method the supplier uses to connect the main incomer. We use 2pole + earth for our domestic systems. Commercial use the same 2pole + earth derived from the 3phase or 3phase +neutral (4 wire) or 3phase +N +E (5 wire)
There are a multiplicity (TT, TN, and lots of others) some just connect the "earth" to "neutral" in the premises others connect the earth to neutral farther upstream. I think some (one?) keeps the earth actually in the earth (ground).
Don't ask me for details, I have only a sketchy recall of the alternatives. See this http://en.wikipedia.org/wiki/Earthing_system |
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| cpemma |
| quote: | Originally posted by Shel-e-bean
Does the UK system use a "neutral"? IE, a main conductor bonded to ground (earth)? |
Neutral is nominally at ground potential, but once in the premises Neutral should be kept separate and a 'Safety Earth' provided, usually connected to the supply cable sheath from the main fuse. In addition, copper central heating/water pipework is connected to the same spot, plus for bathrooms extra rules apply.| quote: | Supplementary Bonding
In a bathroom there are many non-electrical metallic components such as metal baths and basins, supply pipes to bath and basin taps, metal wastepipes, radiators, central heating pipework and so on, all of which could become dangerous if they were to come into contact with a live electrical conductor. To ensure that such an occurrence would blow a fuse or trip a circuit breaker in the consumer unit, Wiring Regulations specify that all these metal components must be connected one to another by an earth conductor which itself is connected to a terminal on the earthing block in the consumer unit. This is known as supplementary bonding and is required for bathrooms even when there is no electrical equipment installed in the room and even though the water and gas pipes are bonded to the consumer’s earth terminal near the consumer unit. When a shower or heater is fitted in a bathroom, that too must be supplementary bonded by connecting its metalwork, such as the casing, to the non-electrical pipework even though the appliance is connected to the earthing conductor in the supply cable. |
http://floti.bell.ac.uk/engapps/domestic.htm |
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| Shel-e-bean |
| quote: | Originally posted by AndrewT
Hi,
our "neutral" varies depending on which method the supplier uses to connect the main incomer. We use 2pole + earth for our domestic systems.
<snip>
See this http://en.wikipedia.org/wiki/Earthing_system |
Thanks for the link. I've looked for something like this at Wiki before, but I never saw this page. One thing I'm not clear on.. Is there a current carrying conductor in a residence (or in appliances) that is at earth potential? The diagrams at Wiki don't show the conductors "in use". In Canada, residences use the "TN-C-S earthing system", and most appliances connect between L1 (or L2) and N, giving them about 110-120 V. Large appliances like stoves and Driers use all three wires, with the heating elements connected across L1 and L2 for 240 V, while motors and timers get 120v. Other things, like large portable tools, might use L1 and L2 and a ground, no Neutral required. Whether a separate ground is used on portable appliances depends on the appliance itself. |
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| AndrewT |
Hi,
Cpemma may have answered, but here goes.
We use live and neutral in our single phase "domestic" system with a protective "earth" (PE).
So all our three pin sockets have L + N + E going back to the distribution board.
Most equipment uses all three wires to ensure safety.
Some equipment is double insulated (classII) and can safely dispense with the earth wire. However our 3pin sockets are shuttered so the double insulated plug top needs a dummy earth pin to open the shutters to allow the plug top to be inserted.
I see a comment in Wikipedia about the (non) safety of the US and Canadian systems for using 2phase (L1 + L2) into higher power equipment. Have you seen that page yet? It was written by a non Brit so no axe to grind. |
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| Shel-e-bean |
| quote: | Originally posted by AndrewT
Hi,
<snip>
I see a comment in Wikipedia about the (non) safety of the US and Canadian systems for using 2phase (L1 + L2) into higher power equipment. Have you seen that page yet? It was written by a non Brit so no axe to grind. |
First, thanks all for the info. :-)
Andrew;
Re the higher power equipment, no I haven't seen that page. As long as there is a safety ground wire, I can't imagine much difference in safety between 120 and 240 V single phase. :-/
Could you find it and post a link? I've tried a few pages without luck. |
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| macboy |
| quote: | Originally posted by Shel-e-bean
I'm not an electronics tech, so my worry with adding a ground wire would be ground loops. Not even new equipment has 3 wire cords... they just use standard polarized 2 wire cords like incandescant lamps. (In the old days, you could get a shock just changing a lamp's bulb if the screw shell was hot. You could plug it in any old way. There was no upside-down). I guess the new equipment is electrically isolated from the mains. To me, the wonderment comes from the fact that tuners aren't like tape players... They need antennas. That involves grounding. My head is spinning. java script:smilie(':xeye:')
xeye |
I agree. Do not add a ground connection, as it invites ground loops.
The power supply for this thing is tranformer coupled, so ground is completely unecessary. The "ground" provided by the secondary of the transformer should be floating, and connected to the chassis. Connecting this to the ground of the power line could cause more problems than it solves (which is: none).
The resistor is a safety measure, as odd as it seems. It is there to prevent the chassis from becoming much higher or lower potential than line. It will not conduct enough to cause a shock. Still, I would use a polarised plug and make sure that the line with the resistor to the chassis is on neutral. I have seen this same thing (with a polarised plug) on a brand-name receiver made around 1998, so it is not a 70's thing. |
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| Shel-e-bean |
Ahh.. The kitchen plug thing. That is the one thing that has had me scratching my head for years. Our old requirements for kitchen counter plugs were truly assinine. They mustn't have asked any electrician experienced in residential service about it.
For the non-Canucks, in kitchens, the counter plugs are "split", the top half of the plug gets one half of a 2 pole breaker, the bottom half of the plug gets the other half of the breaker, and they share the neutral. The outlet halves must be disconnected from each other by snipping the little bar that joins the hots.
I've had numerous calls from people who change their outlets, then can't get the breaker to hold... because they created a short across 240 volts! Sometimes, half the breaker holds and half trips! They might leave it that way for years, too. Or they keep trying to figure it out, and keep blowing the breaker. It's a wonder the breaker stays in one piece. I found one welded closed... Turning it off didn't turn it off!
Ooh ohh.. My favorite.. The "Stab-lok" panels made by FPE are built so you can plug in a 2 pole breaker across 1 phase. All other panels are laid out so that a 2 pole breaker connects across both phases. So if you plug in the kitchen counter breakers across just one phase, the neutral carries double the current. This happens all the time. Inspectors miss it on a regular basis, too. Sometimes the kid wiring the house plugs all the 240 v. breakers in wrong and has to change them because the stove, dryer, hot water tank, baseboard heat etc. is all dead. They will come and fix all the 240 loads, but leave the kitchen breakers! I could go on and on.
Yay for the new code! |
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