Fuses

[bassace]

I was on a gig running a powered speaker cab two days ago and the '13A' plug on the end of the kettle lead blew a fuse. It wasn't necessarily the lead supplied with the cab because, probably like most musos, I have lots of leads all over the place. Anyway I found that the blown fuse was a 3A and probably too low. Strange thing is, the cab doesn't have an in-built fuse and the manual makes no reference.

I'm going to try to standardise all my leads and was thinking of going for a 5A in all of them. Any opinions out there? I've got the correct fuse in each amp, but I don't want to have to use a dedicated lead for each one if I can help it.

[chris_b]

If you increase the fuse then you run the risk of damaging your amp. The 3A fuse did its job and, I assume, protected your amp. I'd replace it with another 3A fuse. The manual should have the required fuses at the back, in the detailed specification section.

[BigRedX]

Watts = Volts * amps.

A quick and dirty rule of thumb is that for amps the input power requirements is twice the output power. Therefore unless power output rating of the powered cab is greater than 400W RMS, the 3 Amp fuse may well be too high.

I'd find the manual and check what the input power requirements are and fuse the lead accordingly.

[chris_b]

My 550 watt Thunderfunk specifies a 3A fuse.

[Mr. Foxen]

Valve amps are less efficient, so the rule doesn't work so well there. My kilowatt Matamp blew a 5amp fuse on turning on, but it has always been happy running with them after that, not so long since it had a proper check up either.

[TimR]

That's unusual to not have an internal fuse. There may well be one that you have to open the amp up to get to.

There's a few conflicting opinions on the forum about the exact purpose of the fuse in the lead.

Generally it is there to protect the lead and putting a 5amp fuse in should be no problem assuming that the lead is rated at 5amp and there is an internal fuse in the amp.

The problem with the cheaper amps at around 500w is that they don't always have soft starts in them and they have big transformers. When you turn them on the fuse can blow due to the big inrush current. They should definitely have a slow blow internal fuse.

Email the manufacturer.

What amp is it?

Edited May 3, 2011 by TimR

[flyfisher]

The fuse in a 13A kettle lead is to protect the lead, not the equipment it's plugged into.

A kettle lead is a component in its own right and can be used with a whole range of other components. The mains plug, the cable and the IEC connector are all specifically designed to safely be used with any compatible devices up to a limit of 13A - including, er, kettles.

If an amp (or anything else) only draws, say, 2A but has a kettle lead connector then the designers must allow for the very likely possibility that someone will use it with a kettle lead containing a 13A fuse - especially in a band environment where all the kettle leads are typically thrown into some sort of box after a gig.

[BigRedX]

One important point that always bugs me in discussions like this. The IEC 60320 connectors/lead found on musical equipment [i][b]ARE NOT THE SAME AS A KETTLE LEAD[/b][/i].

The connectors found on musical equipment are the C13 (female) and C14 (male). They are rated at 15A and up to 70°C temperature. The temperature rating is the important bit, because as you know water boils at 100°C and therefore the connectors used on kettles need to be rated accordingly. The IEC 60320 connectors for kettles are the C15 (female) and C16 (male). They have a temperature rating of 120°C making them suitable for appliances that boil water. Also they are a different shape, the plug having an additional cut out and the socket having a corresponding locator ridge. This means that a lead with a C13 connector which doesn't have the correct temperature rating won't fit into the socket on a kettle.

Only leads with a C15 plug on them are kettle leads, because only they fit a kettle. The leads that came with your musical equipment will all have been fitted with C13 plugs which will not fit the socket on a kettle, and therefore are not kettle leads.

[flyfisher]

Fair point about the technicalities of "kettle leads", but it's a bit like explaining that my Henry vacuum cleaner is not a "Hoover".

Anyway, it doesn't affect the topic of fuses.

[chris_b]

Vertical kettle leads boil the water quicker.

[outsider70]

The used Ashdown ABM 500 RC I bought came without a mains lead.
I asked Ashdown support what fuse rating to use, they told me to use a 13A fuse

[chris_b]

[quote name='outsider70' post='1219974' date='May 4 2011, 03:38 PM']....The used Ashdown ABM 500 RC I bought came without a mains lead.
I asked Ashdown support what fuse rating to use, they told me to use a 13A fuse....[/quote]
They are right. You can do that but then you're relying on the amp's internal fuse for protection. If that blows how do you fix it? If the fuse can't be accessed from the outside of the box you've got to start messing about inside, and maybe on a dark stage!

It's far easier and within most people's grasp of electronics to change a fuse in a plug, or better still use your backup mains lead. You do have one don't you?

[BOD2]

There should be a "power rating" on a plate somewhere on the powered speaker or amplifier that states the INPUT power of the amplifier. It usually says something along the lines of ...

AC 220-240V 50Hz 300W

In this case the maximum power the amplifier would draw in use would be 300 Watts.

To calculate the fuse rating divide this INPUT power (not the OUTPUT power to the speakers) by 240 and choose the fuse rating that is closest to and above this value. Generally, UK mains fuses are available as 1A, 3A, 5A, 10A and 13A.

For this 300W example, a 3A fuse should be suitable, but a 5A fuse might also be used.




However, as stated previously, the fuse in the IEC lead is there to protect the lead itself - not the equipment connected to the lead. The fuse fitted should not exceed the power rating of the cable used in the lead and the IEC connector itself.

The IEC connector (the part that plugs into the amp) should have a maximum current rating embossed on the connector. This will often be 10 Amps or 6 Amps. (10A or 6A, or it may be written as 6/250 which means 6 Amps at 250 Volts etc.). If the IEC connector is molded onto the cable then this will be the power rating for the cable as a whole.


Given that a 5 Amps is equivalent to a power rating of around 1200 Watts (5A x 240V = 1200W) then I would usually fit a 3 Amp or 5 Amp fuse to an IEC lead, unless it was to be used for a very high power amplifier in which case I would ensure that the cable was rated at 10 Amps and fit a 10 Amp or 13 Amp fuse.

If a lower value of fuse (3 Amps or 5 Amps) blows whenever the amplifier is first switched on, then this might indicate that the amplifier has a higher initial surge of power when it first starts up. This may be normal, or it may be a fault condition. In this case I would consult the user manual or manufacturer for advice.

[flyfisher]

[quote name='chris_b' post='1219984' date='May 4 2011, 03:47 PM']They are right. You can do that but then you're relying on the amp's internal fuse for protection. If that blows how do you fix it? If the fuse can't be accessed from the outside of the box you've got to start messing about inside, and maybe on a dark stage!

It's far easier and within most people's grasp of electronics to change a fuse in a plug, or better still use your backup mains lead. You do have one don't you?[/quote]

That's all very well in theory, but what fuse rating are you going to use?

Suppose the amp's internal fuse is 3A. If you fit a high-rated fuse in the mains plug then the internal fuse will still blow first. But if you fit a lower rated fuse (to 'protect' the internal fuse) then you risk it blowing under no-fault conditions.

In my experience, fuses rarely blow for no reason (unless poorly specified) so the chances are that when they blow something else is going to need repairing anyway.

[Dood]

[quote name='BigRedX' post='1219511' date='May 4 2011, 08:45 AM']One important point that always bugs me in discussions like this. The IEC 60320 connectors/lead found on musical equipment [i][b]ARE NOT THE SAME AS A KETTLE LEAD[/b][/i].

The connectors found on musical equipment are the C13 (female) and C14 (male). They are rated at 15A and up to 70°C temperature. The temperature rating is the important bit, because as you know water boils at 100°C and therefore the connectors used on kettles need to be rated accordingly. The IEC 60320 connectors for kettles are the C15 (female) and C16 (male). They have a temperature rating of 120°C making them suitable for appliances that boil water. Also they are a different shape, the plug having an additional cut out and the socket having a corresponding locator ridge. This means that a lead with a C13 connector which doesn't have the correct temperature rating won't fit into the socket on a kettle.

Only leads with a C15 plug on them are kettle leads, because only they fit a kettle. The leads that came with your musical equipment will all have been fitted with C13 plugs which will not fit the socket on a kettle, and therefore are not kettle leads.[/quote]


Thank you! I was just about to go outside and shoot myself! - 'Kettle leads' is a phrase that irks me more than people calling D-Class amplification 'Digital'. - I remember posting such a description of the differences between the two plug and socket types a while back & thank you for doing it his time!

[BigRedX]

I'm glad to see that I'm not the only one dood! For me the phrase is up there on the irritating scale along with "input jack" on a bass when it is most obviously an output jack, and "maple neck" or "rosewood neck" when what is actually meant is maple or rosewood fingerboard.

I actually discovered that the mains lead you use for your amp is not a kettle lead at some point during the 80s when the fuse in my kettle blew and I then discovered that using the mains lead from my amp instead of replacing the fuse wasn't a short cut to getting a pot of tea!

Actually the origin of the phrase "kettle lead" is going to be lost fairly soon as even now I don't think that there are any new kettles being made with C15/C16 mains connectors any more.

[TimR]

This all starts to be very Deja Vue. Have a look at the PAT testing thread it got a bit heavy one hot weekend

Fuses do blow apparently for no reason. Especially in 300-500W amps that don't have soft starts as I said earlier. 300-500W is around the limit that manufacturers trade off cost and practicality.

Every time you turn on your amp you draw between 4 and 10 times the rated current for a fraction of a second as the transformer gets a massive inrush current. It depends where in the cycle the mains is when you turn your amp on. Its random and different each time.

So for a 500W amp you could be pulling 20amps for a fraction of a second. A 5amp fuse will take this maybe a 3 amp one will as well. The internal fuse will be a slow blow or time delay and will take it too.

However, over time, the abuse that these fuses receive each time you switch your amp on will eventually lead to failure. It may be that the amp came with a 3amp fuse after all.

Europeans don't even fuse their leads.

Edited May 4, 2011 by TimR

[bassace]

Thanks for all the helpful replies, guys - and some of the unhelpful ones from those who didn't really read my OP (I said the manual didn't specify any fuse ratings so there's no point in going down that road)

And the 'kettle lead' stuff. It almost turned into a 'god I love jazz' sort of elitism thing. I and most of my colleagues will no doubt refer to them as kettle leads for the rest of time. I recon if I ever came out with 'well, actually, strictly speaking, it's not a kettle lead but blah blah blah blah', then I'd be laughed right off the stage. But I didn''t know the difference so thanks anyway.

I looked at my leads and found that all the UK/euro sourced ones have a 10a rating on the moulded plug-in end. The USA stuff - and all my amps are american - has no such rating. In fact it is my understanding that in the US they never have fuses in the mains plug. So the lead is unprotected. And thanks to the posters who made the point that the fuse is principally for the protection of the lead. However, another fair point was that the fuse gives a certain additional protection to the amp.

My 3a fuse that blew was on the end of a mains lead to a QSC K10 powered speaker rated at 1,000w - so that's probably the reason although of course I wasn't anywhere near that output. Many amps have slow blow fuses to counteract the initial load of transformers and capacitors. As I mentioned, there is nothing in the QSC manual referring to fuses and I can't see any accessible fuse holder on the back. I have emailed QSC's technical support but have not received a reply.

So I am going to fit all my leads with 5a fuses from now. That will provide a sensible compromise between protecting both the lead and amp, and will I hope withstand any start-up surges. Thanks to all who responded, it has widened my understanding of the subject and I hope others have benefitted too.

Edited May 5, 2011 by bassace

[TimR]

A 1000w amp will almost definitely have a soft start or it would be blowing fuses all over the shop. You could try the QSC Forums:
[url="http://forum.qscaudio.com/forum/viewforum.php?f=2&sid=bc8964496154799629d046f4289d8e40"]http://forum.qscaudio.com/forum/viewforum....9d046f4289d8e40[/url]

Edited May 5, 2011 by TimR

[Ross]

Does anyone still actually own a kettle with a lead? I thought they all used detachable bases nowadays?

My amp came without a mains lead, been using a lead I got from maplin for years, no idea what it's rated to, I should probably check.

[flyfisher]

[quote name='bassace' post='1220653' date='May 5 2011, 09:32 AM']Thanks for all the helpful replies, guys - and some of the unhelpful ones from those who didn't really read my OP (I said the manual didn't specify any fuse ratings so there's no point in going down that road)[/quote]

The fact that the manual doesn't specify a fuse rating doesn't necessarily mean it doesn't have an internal fuse. If it's internal then it's not "user serviceable" and will therefore not be covered by the "user" manual. Such things would be covered by the "service" manual though, which is intended for a more technically competent audience.


[quote name='bassace' post='1220653' date='May 5 2011, 09:32 AM']And the 'kettle lead' stuff. It almost turned into a 'god I love jazz' sort of elitism thing. I and most of my colleagues will no doubt refer to them as kettle leads for the rest of time.[/quote]
Indeed. It's just pedantry and not at all relevant to the matter in hand. But you can't argue against pedantry.


[quote name='bassace' post='1220653' date='May 5 2011, 09:32 AM']So I am going to fit all my leads with 5a fuses from now. That will provide a sensible compromise between protecting both the lead and amp, and will I hope withstand any start-up surges.[/quote]
Time will tell.

But it's interesting that this discussion is only really relevant to the UK. I wonder how all those US and mainland European users manage with their completely unfused "kettle leads"?

[quimbymeat]

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