3 prong plug-polarity

[TelZilla]

Im putting a 3prong plug in a BFDR im building. I know the middle/bottom prong goes to ground, but im not sure it matters which side is which for the other two. One side goes to the PT directly, while the other goes through the standby switch.

Does it matter which wire goes where?

 

[Wyatt]

None go to the Standby switch.

The power cord is either Black/White/Green or Brown/Blue/Green (yellow strip)

• The HOT/LINE (Black in the U.S., Brown in most IEC countries) should go to fuse*-->switch-->PT
• The NEUTRAL (White in the U.S., Blue in most IEC countries) goes to the PT
• The GROUND/EARTH is Green

You'll find IEC jacks are labelled L, N, E (Line, Neutral, Earth)

Since it's AC, the PT is not polarized, either end of the primary can go to LINE or NEUTRAL.

*On the traditional bayonet fuse holders, the HOT/LINE goes to the tip of the fuse holder.

 

[jhundt]

Just what Wyatt said, and I will add this:

almost all modern amps sold in Europe will have a double-pole power switch, and both the hot and neutral will be switched. This is a safety feature; many European plugs and sockets are symmetrical, allowing the plug to be introduced with the hot and neutral reversed.

 

[robrob]

Polarity does matter. You want the hot wire going to the fuse center terminal.

image removed

Modern U.S. wall cords and sockets have a narrow blade for Hot (black wire 120v), a wide blade for Neutral (white wire ground), and a round or 'D' shaped prong for the chassis Safety Ground (green wire ground). Power cord wire colors are sometimes non-standard so use a multimeter to identify Hot and Neutral. Europeans sometimes use the letters E: Earth (safety ground), L: Line (hot) and N: Neutral to describe the three plug wires.

 

[clintj]

To further elaborate, you want the hot going to the fuse first for your safety. In the event the amp has an issue, the fuse blowing will cut all power to the amp by breaking the circuit right where it enters. If the neutral is fused, it will still blow on overcurrent. However, the hot lead can still pass current through the chassis to ground - either via the ground wire or through you.

 

[24 track]

to add to what was said above wall current in North america flows from Black to white so if the fuse is on the black (hot) the fuse will prevent current to flow past the fuse, If the Nuetral is on the fuse current is still present and flowing in your circuit. and that is the start of the circuit, deadly voltages are still present in your amp after the power is turned off so be carefull

 

[ColonelPanic]

Not sure if it's a cultural thing (or just nitpicking) but we call the hot wire (black in your case) "live" rather than "line".

Either way, it's best practise (for your safety) to run that side into the fused side of the amp.

 

[robrob]

In Europe the IEC says L is for Line. For 3 phase electrical they specify Line 1, 2 and 3. 'Live' is a commonly used slang term.

 

[BobbyZ]

I like to check the continuity on power cords. Just to make darn sure wires go where they're supposed to on the plug. Also if you salvage old computer IEC cords they almost always have different colors than the US standard. So you either Google all day trying to figure it out or check continuity, hook it up and get on with other things.

 

[jhundt]

hot, neutral, and a ground... same as it's ever been, same as it's ever been...

 

[24 track]

I like to check the continuity on power cords. Just to make darn sure wires go where they're supposed to on the plug. Also if you salvage old computer IEC cords they almost always have different colors than the US standard. So you either Google all day trying to figure it out or check continuity, hook it up and get on with other things.

30 seconds with multimeter and your in,

 

[BobbyZ]

hot, neutral, and a ground... same as it's ever been, same as it's ever been...

Exactly but I don't trust that green, black and white wires always go to the right prongs on a molded plug.
Haven't found one that didn't but I still check.

I get shocked enough with my own stupidity.

 

[jhundt]

I agree, I check everything too. and I forget what it's supposed to be and I have to look it up again, every time...

 

[robrob]

"Hot black chicks" helps me remember which wire is hot.

 

[Silverface]

many European plugs and sockets are symmetrical, allowing the plug to be introduced with the hot and neutral reversed.

I don't see how this is possible with a 3-prong plug. Are you saying they have a second ground socket so there 1re FOUR outlets - two blade and two round or oblong?

 

[jhundt]

image removed
here you can see a wall socket, and two plugs.
if you look at the wall socket, you will see two round holes, those are the live and neutral contacts. At the top and bottom of the socket you see two bare metal spring contacts; these are the earth (ground) contacts.
the plugs could be removed, turned 180 degrees and reinserted.

So it's not a really a three-PRONG plug, but a three-connection plug.

But you can never be sure which side is hot and which is neutral without testing.

So most devices use a double pole switch which interrupts both sides.

 

[flow]

So when you are in Europe with the above mentioned three-connection plugs, which can be inserted both ways (so you never know what is hot or neutral) would this be an adequate way of wiring an old Fender head? Do I need to replace the Power Switch with a DPST type to switch both hot and neutral at the same time, to be safe? But the fuse would still be installed before the switch?

I just changed the standard 3prong conversion schematic to illustrate what i mean.

 

[Bill Moore]

jhundt, what voltage is supplied from the socket in your picture? I thought most of Europe was 220-240V. if so it makes no difference the connection, as both prongs are hot.
It seems an adapter would be needed to power USA devices, will the adapter substitute the (earth) ground for the neutral connection to get the desired voltage?

 

[jhundt]

no, Bill, over here both prongs are not hot on a 220/240V circuit. There is one live wire at 240V, and one neutral wire at 0V - just like the USA only twice the voltage.

flow - that looks like how I would do it.

 

[Bill Moore]

Thanks for the knowledge!