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Author Topic: Double fusing  (Read 4130 times)
AA4PB
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Posts: 12854




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« Reply #15 on: December 01, 2012, 05:51:49 PM »

"OTOH as I recall both Ford & GM engineering bulletins call for protecting both leads."

How come the auto mfgs don't fuse the negative connection to all of their electronics like the car radio, etc?
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STAYVERTICAL
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Posts: 873




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« Reply #16 on: December 01, 2012, 05:54:29 PM »

I can see some of the arguments for double fusing, but it does seem a bit far fetched for most halfway competent  hams in mobile operation.

However, as 4WC stated, NEVER double fuse a mains circuit in normal household use.
It is illegal in most countries, since you want to disconnect the active lead of the mains from the equipment in the event of a fuse blowing.

12 volts is one thing, 110/240 V.A.C is another thing entirely.
It can easily kill you or others if you are not careful.

Take care,

73 - Rob
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W6EM
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Posts: 800




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« Reply #17 on: December 01, 2012, 08:13:48 PM »

However, as 4WC stated, NEVER double fuse a mains circuit in normal household use.
It is illegal in most countries, since you want to disconnect the active lead of the mains from the equipment in the event of a fuse blowing.

The terminology might get in the way, but when you say a "mains" circuit, that could also mean a 240V circuit, which consists of two hot legs, (each being 120V to ground) and both are to be fuse or breaker protected.

In our US 115-120VAC system, the neutral is single-point grounded at the main panel and at no other place in your dwelling.  It's also grounded at the utility transformer and any attached neighborhood homes.  If a neutral is opened and the hot leg is not also opened simultaneously, it could leave appliances energized or hot, when thought to be turned off.  A three-way circuit is the only exception where switching of what consistitutes a neutral is permitted.

Neutrals are not at zero volts potential unless no net current is flowing through them.  Where running through a dwelling, the neutral voltage at any point is at least the IZ drop in the neutral wire at that point back to your main panel.  That, under the assumption that your net neutral current back to the utility transformer is zero amps.
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K1CJS
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« Reply #18 on: December 02, 2012, 07:36:56 AM »

One other thing to mention.  Most people have the inside of their hood opened at least once every couple of weeks to check the fluid levels and the engine accessories.  It's a simple matter to get into the habit of checking the state of the battery terminals, the battery connections and the fused connections as well when you do have the hood open. 

If you have your car looked at at a service center, just ask them to check the battery and the accompanying connections including the fuses.

That is one extremely simple point that would eliminate all the arguments about fuses blowing and you not realizing it!
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N4CR
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Posts: 1668




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« Reply #19 on: December 06, 2012, 07:23:39 PM »

One other thing to mention.  Most people have the inside of their hood opened at least once every couple of weeks to check the fluid levels and the engine accessories.  It's a simple matter to get into the habit of checking the state of the battery terminals, the battery connections and the fused connections as well when you do have the hood open. 

If you have your car looked at at a service center, just ask them to check the battery and the accompanying connections including the fuses.

That is one extremely simple point that would eliminate all the arguments about fuses blowing and you not realizing it!

That's not the only ground. The engine block ground carries the return current for the starter. If that opens, it's going to try to find another path. When was the last time everyone here checked their engine block ground?
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KA4POL
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Posts: 1995




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« Reply #20 on: December 06, 2012, 09:53:22 PM »

I notice most modern transceivers use dual fuses one in the positive leg and one in the negative leg.
My IC-1271 already has dual fuses in the power supply cable and it dates back from the eighties of the last century.
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K4JJL
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Posts: 489




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« Reply #21 on: December 07, 2012, 11:33:46 AM »

Some of the ideas in the article are pretty far fetched...  Commercial radios are typically not fused on the negative lead, simply because you don't want a situation where you loose the grounding. 

Most commercial radios have a 3' negative lead and a 20' positive lead.  In my truck, the positive is run all the way to the battery from the back seat.  The negative is tied directly to a seat bolt next to the radio.
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W6EM
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Posts: 800




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« Reply #22 on: December 07, 2012, 07:13:22 PM »

Some of the ideas in the article are pretty far fetched...  Commercial radios are typically not fused on the negative lead, simply because you don't want a situation where you loose the grounding. 

Most commercial radios have a 3' negative lead and a 20' positive lead.  In my truck, the positive is run all the way to the battery from the back seat.  The negative is tied directly to a seat bolt next to the radio.

Here's the problem with body bolt attachments.  Ones which penetrate the body to the underside are subject to corrosion from road salts, salt water, etc.  And, over time, the same can be said for negative terminal to body jumpers under the hood, unless protected by sealants, paint, etc., as applied by the manufacturer.
If you want to get the best body-return, the connection to the body should be through body metal that is totally inside the vehicle without penetration to the outside.
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K1CJS
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Posts: 6034




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« Reply #23 on: December 08, 2012, 07:06:31 AM »

Most commercial radios have a 3' negative lead and a 20' positive lead.  In my truck, the positive is run all the way to the battery from the back seat.  The negative is tied directly to a seat bolt next to the radio.

Every Kenwood commercial radio that I've seen has a six foot two wire harness--with fuses on both power leads.  The only radios I've seen under your description were specially ordered that way, and those were the old type trunk mounted radios.
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