ProSoundWeb Community
Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Mike Sokol on February 14, 2015, 03:05:18 PM
-
So here's an old Bassman 70 head I had kicking around in the closet. I'm going to clean it up and make it safe for my tube amp experiments. As you can see it's an oldie with a stinger cap selector as well as a broken off ground pin on the power cord. IIRC this thing sounded pretty great the last time I fired it up (maybe 15 years ago) so it should be fun to get it going again.
Oh yes, I'm going to replace the power cord for one with a correctly grounded plug and check it over for ground leakage currents before I hand it over to my guitar player. And since I'm picking up an original Shure Green Bullet mic next week that just needs a new connector soldered on the cable, this will make a great harmonica amp as well. I also have the cabinet for it with a 12" Celestion Seventy-80 speaker that should match up nicely. I'll let you know how it sounds after I get it all cleaned up.
-
I assume you can still plug it in with a broken off earth pin.
Something I like about our UK sockets is that they have shutters over the live and neutral holes which prevents children (and us bigger children) from pushing in metal objects and getting electrocuted.
The shutters move out of the way when the earth pin is inserted. This has two advantages: 1. The earth is the first to connect and the last to disconnect and 2. you can't insert a plug with a broken earth pin.
Steve.
-
I assume you can still plug it in with a broken off earth pin.
Something I like about our UK sockets is that they have shutters over the live and neutral holes which prevents children (and us bigger children) from pushing in metal objects and getting electrocuted.
The shutters move out of the way when the earth pin is inserted. This has two advantages: 1. The earth is the first to connect and the last to disconnect and 2. you can't insert a plug with a broken earth pin.
Steve.
Steve, we have no shutters on the ground in the USA, so we're free to plug in anything with a broken off ground pin and kill ourselves.
-
Residential is now required to use tamper resistant which have shutters-but no connection/requirement for ground pin-just hot and neutral at the same time. Of course, locking out for a missing ground pin also eliminates the possibility of using 2 wire plugs for double insulated appliances.
-
Of course, locking out for a missing ground pin also eliminates the possibility of using 2 wire plugs for double insulated appliances.
I have posted before about how the US seems to have a bewildering assortment of plugs for domestic equipment. Here we have just one. The 13 amp three pin plug. Every socket/outlet in a domestic building and the majority in commercial buildings (apart from industrial outlets) will be the matching 13 amp three pin socket.
Double insulated equipment with no earth connection uses the same plug but the earth pin is not connected.
The only variance is the fuse within the plug which could be 2A, 3A, 5A, 10A or 13A depending on load.
Steve.
-
The US has receptacles with shutters. They are labeled 'TR' (Tamper Resistant) but they only require the the Hot & Neutral be inserted at the same time, the Ground pin is not involved in opening the shutters. Many new wall-warts only have two non-polarized pins.
-
I have posted before about how the US seems to have a bewildering assortment of plugs for domestic equipment. Here we have just one.
We only have 1-the Edison with 3 pins-hot-neutral and ground. However it is available in 2 configurations-the 20A (which you can plug a 20A plug or a 15A plug) and the most common standard 15A.
Decades ago you could find 2 pin edisons (no ground), but they are rare these days (only in older buildings).
You find this in all the houses-businesses etc. You can plug ground or ungrounded equipment into them.
However once you get to 20A or more-it all changes. There start to be all kinds of varieties-120V, 240V, twistlock straight pins-different combinations of straight pins etc.
You mentioned the shutter on your plugs. Do your "wall warts" or line lumps" all have 3 pins? Most of ours do not have a ground pin. It is the rare one that does have a ground pin.
-
You mentioned the shutter on your plugs. Do your "wall warts" or line lumps" all have 3 pins?
They have a pin... but it's usually plastic!
(http://i.ebayimg.com/00/s/MTYwMFgxNDE3/z/CtgAAMXQTT9Rue1D/$%28KGrHqRHJCoFEPQh86edBRue1DRQ5Q~~60_35.JPG)
Unfortunately, being plastic makes it easier to break them off. Then they don't go into the socket unless you open the shutters by pushing a screwdriver into the earth aperture... apparently!
Steve.
-
I'm also working on an Ampeg VT40 that I let someone trade to me for a repair about 20 years ago. Time to put a grounded power plug on this thing and fire it up. This is an old 1970's tube amp with 60 watts output and no master volume control, so it was really LOUD the last time I tested it. I'm going down my inventory of closet tube amps and making them all safe by correcting the grounds including my vintage Ampeg SVT head. Now THAT'S a beast to move around.
IIRC one of the first things I did with my 1954 Hammond B3 was add a grounded power plug. That was around 1974 and it only took one good shock to convince me that it needed to be grounded.
-
The shutters move out of the way when the earth pin is inserted. This has two advantages: 1. The earth is the first to connect and the last to disconnect and 2. you can't insert a plug with a broken earth pin.
Here's a little more on how that works. I have some experience with British plugs since I've run the Malcolm Hill AC-DC (the band) PA system here in the USA for many years. It used a sometimes bewildering array of 230-volt UK and 120-volt USA power plugs. Note that the UK plug has insulated sleeves that won't allow you to make contact with the metal contacts if the plug is pulled halfway out of the socket. Of course a USA/Edison plug doesn't have that protection so you have to watch your fingers while plugging in. And the fuse inside of the input plug prevents a consumer from overloading an extension cord. In the USA there's nothing to stop you from plugging a 15 amp space heater into an extension lamp cord rated for 8 amps. That's probably why we have so many space heater fires in the USA when the temp goes down.
Yes, the UK plug is vastly safer than the USA/Edison version, but don't expect any changes to the NEC overnight. I'm still replacing 1923 wiring in my house.
-
In the USA there's nothing to stop you from plugging a 15 amp space heater into an extension lamp cord rated for 8 amps. That's probably why we have so many space heater fires in the USA when the temp goes down.
Yes, the UK plug is vastly safer than the USA/Edison version, but don't expect any changes to the NEC overnight. I'm still replacing 1923 wiring in my house.
Also we can plug a electric blanket with tiny wires that get kicked and pushed around all night into a outlet that is protected with a 20 amp breaker. Years ago I called my insurance company and told them "I know this sounds unbelievable but my electric blanket caught fire." They replied no problem, quite believable. We get a tremendous amount of clams for fires started by electric blankets and electric coffee makers.
-
Also we can plug a electric blanket with tiny wires that get kicked and pushed around all night into a outlet that is protected with a 20 amp breaker. Years ago I called my insurance company and told them "I know this sounds unbelievable but my electric blanket caught fire." They replied no problem, quite believable. We get a tremendous amount of clams for fires started by electric blankets and electric coffee makers.
That's why I got rid of my electric blanket, and won't buy another. Mine never caught fire, but I've heard too many horror stories, and the risk seems too great to me. Better to insulate your bedroom and use a regular heater.