Voltage drops to less than half under load of a 40watt exhaust fan.

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Old 03-20-16, 07:44 AM
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Voltage drops to less than half under load of a 40watt exhaust fan.

I live in Madagascar, where the wiring on our house (and most others across the country) is atrocious - with no enforced building regs and electricians as scarce as hen's teeth! I am about to replace an exhaust fan in the kitchen, but found that the voltage in the live circuit is 200 volts (supposed to be 240) but it drops to 97 volts when the exhaust fan switch is turned on, and the fan spins VERY slowly. Any suggestions as to what is happening? Could the hot and neutral be switched somewhere in one of the kitchen circuits?

TIA, Colin.
 
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Old 03-20-16, 08:30 AM
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Welcome to the forums!

This is mainly a US site but we might be able you help you out.

It sounds like you have a meter and know how to use it so that is helpful. It sounds to me like you have a open connection someplace and the fan is in series with some other device. This could be as small as a loose connection in a junction box, or a big as as bad connection on your incoming power from the pole.

Is your issue only with the fan, or is there other odd electrical issues elsewhere in the house?
 
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Old 03-20-16, 09:50 AM
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I would check for poor connections. Often I see one wire just wrapped around another to make a connection. Over time a layer of oxide (tarnish) develops on the wire surface that increases the resistance across the connection. Not only does it cut the voltage downstream but that lost current is converted to heat at the connection point... think fire.
 
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Old 03-20-16, 10:51 AM
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Hi Tolyn Ironhand and thanks for the welcome!

Unfortunately, the house and our school buildings are filled with "odd electrical issues" and anomalies. There are no grounded wires anywhere, so no true neutrals. In the kitchen, the neutral wires can run from 30 to 50 volts at any one time. I spoke to a utilities company repairman following a cyclone and asked if he could install a ground wire at the main junction box, but he said we didn't need it. The following year, another cyclone came through and following a lightning strike, a three phase pole toppled over, sending a surge through our electrical system and leaving 380 volts running in the live wire and 120 in the neutral, leaving a number of short-circuits as they had originally embedded wires directly into the concrete with no conduit pipes, leaving an electrical nightmare. We have just disconnected the circuits with problems and live withougt them until we can find someone we trust to re-wire much of the house!

I had not thought about the cause in this particular circuit as being a loose connection, but that may well be a possibility I will need to check out, both in the kitchen and at the mains box.

Also is there any problem if I were to install a copper earth rod at the mains box? It appears the utilities company does not have an earthed connection anywhere near us (even though their three-phase high voltage line is only 5 metres from our property), so I am not sure what happens in their high voltage lines if I earth the single phase line at my junction box. Any suggestions? I am also thinking of also doing the same for the kitchen circuits, earthing it out to the water pipes or an external copper rod. Suggestions?

Thanks again,

Colin.
 
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Old 03-20-16, 10:55 AM
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Hi Pilot Dane!

Thanks for your reply, and yes, that is a problem throughout the electrical system on our compound! Thinking of fire risk certainly does raise the priority level for finding a permanent solution! The next blackout (which are every day or so here!) I need to be more methodical in checking for loose connections. Thanks for the reminder, and I will see if it is part of the problem for this particular exhause fan.

Thanks again,

Colin.
 
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Old 03-20-16, 11:06 AM
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I do not think a ground rod will have any benefit other then to dissipate surge voltage from lightning or storms like you mentioned. I can't really say where to connect it if you truly do not have a grounded conductor (neutral) in your electrical service. Also, if there is nothing grounded on their three phase pole where would the stray voltage go?

Do you see a wire coming down the pole into the ground?
 
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Old 03-20-16, 11:17 AM
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No, there is nothing there! I pointed this out the last time the utility company guy was here to replace the pole, and he just laughed at my request to install a ground, adding that virtually NONE of the poles in our city are earthed! Great consolation for me!

Colin
 
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Old 03-20-16, 11:32 AM
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Then there is really no point to add a ground rod.
 
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Old 03-20-16, 04:00 PM
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Would adding a ground rod to the kitchen circuit eliminate the 30-50 volts currently in the neutral wire. Is there any way to make the house neutral circuits independent of the mains? With a one-way diode or something similar?

Thanks again!

Colin.
 
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Old 03-20-16, 04:51 PM
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Would adding a ground rod to the kitchen circuit eliminate the 30-50 volts currently in the neutral wire.
No. Again, a ground rod is only for high voltage events such as lightning strikes. It is not designed to carry current.

There are no grounded wires anywhere, so no true neutrals.
I am not familiar to how things are wired in Madagascar so you have to take my advice with a grain of sand. Between what two points are you measuring voltage on the neutral if nothing is grounded? What type of meter are you using? Digital? 30-50 volts is not outside the realm of phantom voltage. It is also possible that you are reading through another appliance that is in series as I mentioned before, with an open neutral.

Is there any way to make the house neutral circuits independent of the mains?
I'm not sure what you mean by that. In a normal US single phase service the neutral is center taped on the transformer. The two hots are 240 volts between them, and each hot to neutral is 120 volts. I would image that your service is similar, although you said there is a three phase pole near you, but with just different/higher voltages.

Maybe it would be a good idea to take some pictures of your electrical service (being very careful) with the panel cover off so we can see what you have going on. If you want, you can post them to a site like photobucket and then link them here.
 
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Old 03-20-16, 06:43 PM
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If a utility pole falls or twists causing large power surges then a ground would probably not have prevented damage to the wiring. What happens is that the utility pole probably had some medium tension lines, called primary lines, up top; they carry several thousand volts. The 240 volt or 120 volts lines are called secondary lines and get their power from transformers on the poles in turn fed by the primary lines.

Should the multi-thousand volt primary touch one of the secondaries then house wires connected to those secondaries can be badly fried, short circuiting to one another in a conduit or in a trough in a concrete wall or within a plastic sheathed cable.

Identify the primary connections (usually with larger insulators on the transformer body) and the secondary connections (usually with smaller insulators).

One of the primary connections and one of the secondary connections might have no insulator. These would be the neutrals. In grounded systems, the neutral of the primary is connected to the neutral of the secondary and also to ground wires strung from pole to pole and ground rods on some if not all poles.

The transformer may have either two of three secondary connections. Your house may have just two wires coming from the pole or may have three wires. If there are three wires, you will probably measure 240 volts (120 in the U.S.) between two combinations of two at a time and 480 volts between the other combination. The neutral is the wire left out when you measured the 480 volts (240 in the U.S.). If you have just two wires coming to your house from the pole, you will have to find other landmarks such as one connected to the transformer with no insulator to identify it as neutral.
 
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Old 03-20-16, 06:58 PM
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If you wnat to, you can decide not to bother to find out which of the two wires (if just two come to your house) is neutral. You will have to assume (actually correctly) that both are hot. If either has a loose connection then things will not work. The system will work correctly with no ground.


But be careful when changing things around because at some time you will succeed in identifying the neutral or at some time in the future the power company will put in grounding which in turn will designate one of the two wires coming to your house as the real neutral. Your own tinkering must not depend on one wire definitely being the neutral unless you find out for sure that it is the neutral right now.

To repeat, if you have 3 wires coming from the utiligy pole with 480 volts between two of them then the third wire is defrinitley the neutral. The neutral should have 240 volts measured to either hot wire. If the neutral has a loose connection in this case you can have unpredictable and changing voltages that will fry electronic equipment.

Do not connect a ground rod to any wiring that you have not identified as neutral such as using inspection out to the utility pole.
 

Last edited by AllanJ; 03-20-16 at 07:17 PM.
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Old 03-20-16, 07:25 PM
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In the U.S. "neutral" stands for the portion of the wiring that is grounded (aka earthed). If you cannot identify for sure which of the wires from the pole (if just two) entering your house is a neutral, do not connect up a ground rod. It is possible that the power company may in the future designate the other wire to be the neutral and your ground rod will then cause all kinds of problems.
 
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Old 03-20-16, 07:32 PM
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The transformer may have either two or three connections, not two of three connections. Forum won' t let me edit that, giving me just a blank white page my text and I can't type into it.
 
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Old 03-20-16, 08:30 PM
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What you probably have is like a 240 branch circuit in the U.S. In the U.S. a 240 single phase branch circuit has no neutral. Neutral is just a term for a hot wire that has been grounded but a hot wire doesn't need to be grounded to work.
 

Last edited by ray2047; 03-20-16 at 10:29 PM. Reason: Clarify.
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Old 03-20-16, 09:11 PM
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In the U.S. a 240 single phase has no neutral.
In a 120/240 volt single phase system the grounded conductor is "neutral" meaning it has equal potential between it and all the ungrounded conductors. The only time time that the grounded conductor is not "neutral" would be in 120/240 volt delta high leg system, or an open delta system. We still call it a neutral just for simplicity sake.

In the U.S. "neutral" stands for the portion of the wiring that is grounded (aka earthed)
It is also the conductor that is connected to the midpoint of the transformer(s)
 
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Old 03-20-16, 10:28 PM
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To clarify I meant a 240 volt branch circuit.
 
 

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