Placing Rectifier Diode in Neutral Wire of House Wiring

Thread Starter

PeteHL

Joined Dec 17, 2014
363
Standard house wiring includes the practice of not inserting any device such as a switch or a fuse between a load and the neutral wire. What I would like to do is insert a a paralleled pair of rectifier diodes between a load and the neutral wire. The diodes are connected anode to cathode in parallel so that there is a small voltage drop across the pair and there is largely no disruption of current to the load. As this is against standard practice, I'm wondering if it doing this could be harmful in some way?

As the neutral wire is connected to ground at the service entrance, this does mean, doesn't it, that I can touch either side of the diode pair and not receive a shock?

I'm not going to post the entire circuit including the inserted diodes as I believe this might lead to describing a circuit that could be potentially harmful for anyone who does not fully understand the possible hazards of the circuit.

Regards,
Pete
 

nsaspook

Joined Aug 27, 2009
8,688
A load overload or short could pop those diodes (acting as a fuse during high current faults) long before the utility beaker or line fuse pops leaving a possible dangerous condition on any circuit that depends on the diodes being functional. I wouldn't do it. It pays to be paranoid. People will assume that Neutral is at near zero volts but don't bet your life on it.
240.22 Grounded Conductor. No overcurrent device shall
be connected in series with any conductor that is intentionally
grounded, unless one of the following two conditions is met:
(1) The overcurrent device opens all conductors of the circuit,
including the grounded conductor, and is designed
so that no pole can operate independently.
(2) Where required by 430.36 or 430.37 for motor overload
protection.
 
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Thread Starter

PeteHL

Joined Dec 17, 2014
363
A load overload or short could pop those diodes (acting as a fuse) long before the utility beaker or line fuse pops leaving a possible dangerous condition on any circuit that depends on the diodes being functional. I wouldn't do it. It pays to be paranoid. People will assume that Neutral is at near zero volts but don't bet your life on it.
Thank you; good point. Also, if the diodes failed and became an open circuit, and the circuit breaker isn't tripped, then the hot wire connected to the load remains live.
 

Ian0

Joined Aug 7, 2020
3,281
Standard house wiring includes the practice of not inserting any device such as a switch or a fuse between a load and the neutral wire. What I would like to do is insert a a paralleled pair of rectifier diodes between a load and the neutral wire. The diodes are connected anode to cathode in parallel so that there is a small voltage drop across the pair and there is largely no disruption of current to the load. As this is against standard practice, I'm wondering if it doing this could be harmful in some way?

As the neutral wire is connected to ground at the service entrance, this does mean, doesn't it, that I can touch either side of the diode pair and not receive a shock?

I'm not going to post the entire circuit including the inserted diodes as I believe this might lead to describing a circuit that could be potentially harmful for anyone who does not fully understand the possible hazards of the circuit.

Regards,
Pete
Why?
 

DickCappels

Joined Aug 21, 2008
7,746
Because opening a switch in series with neutral would leave the entire circuit floating on the line.

My guess is that the true reason is that is what electrical codes say.
 

Ian0

Joined Aug 7, 2020
3,281
I'm not advocating that it is in any way a sensible thing to do, but:
Neutral is regarded as live for determining safety, so having the entire circuit floating at live potential isn't that dangerous - plenty of countries (most of continental Europe) have mains connectors where live and neutral are reversible.
I see the possibility of one diode failing open as being the biggest potential problem - that would leave the entire circuit on a half-wave rectified supply, and lots of appliances with transformers may catch fire.
I would expect an overloaded diode to fail short rather than open, which would fail safe.
I'm waiting with bated breath to find out why anyone would want to put two antiparallel diodes in the neutral supply. . .
 

andrewmm

Joined Feb 25, 2011
1,757
regarding neutral being earth,
Our house, at various times, depending upon weather et all, you can get a shock off neutral ( but not the gnd )

I'd love to know why you want to put a 0.6 v drop in the neutral,
I am having problems thinking wat your doing that can not be done in a more conventional / safe way.
 

Ian0

Joined Aug 7, 2020
3,281
Yes, it does sound like he wants to use the diodes to measure AC mains current
Really? It's a tricky way of measuring current! V varies as log(I), along with a variation with temperature.
If he were going to put anything in series with the neutral to measure current it would be a resistance (a shunt).
Current transformer would be the way to go (if indeed he wants to measure the current)
 

crutschow

Joined Mar 14, 2008
27,761
Really? It's a tricky way of measuring current! V varies as log(I), along with a variation with temperature.
The diodes would prevent possible damage to a low voltage-drop ammeter shunt in parallel with the diodes for a large overload or short until the breaker blows.
 

dendad

Joined Feb 20, 2016
3,914
The diodes would prevent possible damage to a low voltage-drop ammeter shunt in parallel with the diodes for a large overload or short until the breaker blows.
I would expect the diodes would blow long before the shunt would. But the protection of something may be what the TS is thinking. He has not really explained the function, but whatever the proposed reason, it is not at all an good idea.
 

Thread Starter

PeteHL

Joined Dec 17, 2014
363
I'm waiting with bated breath to find out why anyone would want to put two antiparallel diodes in the neutral supply. . .
Yesterday I got an email from the person who proposed the diodes current-sensor. He also suggested alternatively using a current transformer.

At my place there are two heating cables, one placed along the exterior of water pipes, the other is inside the line (pipe) from the well to the pressure tank. The heating cable exterior to pipes I control remotely as there isn't any provision of a manual switch for it at this house that I bought second-hand. So especially with the one that I turn off when the air temperature is high enough that it isn't needed, for peace of mind, I like an indicator showing that it is actually heating. It is crucial that the one inside the pipe is working when it's cold, so I want to keep an eye on that one also.

I would show the entire circuit, but I,m not certain that AAC would approve of me showing it, as to some extent there is not-isolated AC voltage in the circuit. Some years ago I posted such a circuit here and was told that that shouldn't be posted. So I don't want to be a repeat offender :confused: -Pete.
 
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MisterBill2

Joined Jan 23, 2018
9,308
The current transformer is by far the best choice, and since it does not need to be very accurate to detect off or ON, it is a simple matter to make one that is adequate for sensing off and on. With enough turns a current transformer can light an LED indicator to let you know a current is flowing. Totally isolated plus low voltage plus no need for external power, it is about as safe as it can get.
 

MisterBill2

Joined Jan 23, 2018
9,308
Certainly this is true. And if that need is preent then a voltmeter across the CT (Current Transformer) will allow a quick comparison with what is known to be correct operation.
But so far we are given no details and no clues.
And a simple cheap CT can be made from a half inch section of iron pipe and a few feet of thin insulated wire. The hard part is filing the burrs off of the iron pipe to avoid scraping the wire insulation.
 
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