Which leg to fuse - Line or Neutral?

tommytube · 25th May 2008, 06:14 PM

In building an amp, which leg should be fused on the incoming AC lines? Line or neutral? This is for USA, 110Vac.

Is the answer any different depending on what topology amp I'm building? Does a typical SS bipolar amp fuse the same as a chip amp and the same as a tube amp? What consideration should be part of the analysis?

I think I've seen it both ways and always wondered if there was a preference related to AC theory.

TIA,
Tommytube

pooge · 25th May 2008, 07:09 PM

Line

jaycee · 26th May 2008, 01:52 AM

It should always be Line/Live/Active.

Tony · 26th May 2008, 01:57 AM

Line

VivaVee · 26th May 2008, 01:58 AM

UL60950 listing/approval requires the fuse in the active/phase line. They used to only accept a wired fuse but will now accept a MCB as well.

As you are in the US it seems good practice to follow this recommended practice.

Leolabs · 26th May 2008, 02:22 AM

No doubt,it's line.

CBS240 · 26th May 2008, 05:48 AM

Hi

Round hole is earth GND, large slit is neutral (white), small slit is hot (black), line, live, ect. Fuse the hot as everyone has stated. Properly grounding the case to earth is important too. There's no guarantee that every home outlet is wired properly.

Therefore, "Safety first" when it comes to line voltage is a good tune, IMHO.

You are using an isolation transformer, so obviously there should be a fuse on the primary winding. If you are not using isolation, then you are committing a grave error and we do not discuss non-isolated circuits for audio here.

peranders · 26th May 2008, 06:47 AM

Quote:

Originally posted by Leolabs
No doubt,it's line.

Only in a country where you keep this things in mind. In many parts in Europe you don't distinguish line and neutral. You can turn the plug 180 degrees.

pooge · 26th May 2008, 02:15 PM

Quote:

Originally posted by peranders

Only in a country where you keep this things in mind. In many parts in Europe you don't distinguish line and neutral. You can turn the plug 180 degrees.

Then that would be line-line and not line-neutral

audio-kraut · 26th May 2008, 02:40 PM

Quote:

Then that would be line-line and not line-neutral

how do you figure?

L (receptacle) ----- hot amp

N (receptacle) ----- n amp

turn 180

N (receptacle) ----- hot amp

L(receptacle) ------- n - amp

am I missing something in your answer?

Anyway, the question was asked by a citizen of the US, and we (North Americans) have polarized plugs for the reason to clearly identify N and L contacts.
Neutral is silver coloured, hot golden, ground screw green.

Wire your plug wrong (in a new house construction) - and the electrical inspectors comes down on you like a sledgehammer.

25th May 2008, 06:14 PM	#1
tommytube diyAudio Member Join Date: Sep 2004 Location: Eastern Oregon	Which leg to fuse - Line or Neutral? In building an amp, which leg should be fused on the incoming AC lines? Line or neutral? This is for USA, 110Vac. Is the answer any different depending on what topology amp I'm building? Does a typical SS bipolar amp fuse the same as a chip amp and the same as a tube amp? What consideration should be part of the analysis? I think I've seen it both ways and always wondered if there was a preference related to AC theory. TIA, Tommytube

26th May 2008, 01:57 AM	#4
Tony diyAudio Member Join Date: May 2003 Location: Palatiw, Pasig City	Line __________________ http://www.electronicslab.ph/forum/i...?topic=32688.0

26th May 2008, 01:58 AM	#5
VivaVee diyAudio Member Join Date: Jun 2004 Location: Auckland, NZ	UL60950 listing/approval requires the fuse in the active/phase line. They used to only accept a wired fuse but will now accept a MCB as well. As you are in the US it seems good practice to follow this recommended practice. __________________ Alan

26th May 2008, 05:48 AM	#7
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Hi Round hole is earth GND, large slit is neutral (white), small slit is hot (black), line, live, ect. Fuse the hot as everyone has stated. Properly grounding the case to earth is important too. There's no guarantee that every home outlet is wired properly. Therefore, "Safety first" when it comes to line voltage is a good tune, IMHO. You are using an isolation transformer, so obviously there should be a fuse on the primary winding. If you are not using isolation, then you are committing a grave error and we do not discuss non-isolated circuits for audio here. __________________ All the trouble I've ever been in started out as fun......

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25th May 2008, 07:09 PM	#2
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	Line

26th May 2008, 01:52 AM	#3
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	It should always be Line/Live/Active.

26th May 2008, 02:22 AM	#6
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	No doubt,it's line.

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