House wiring

[Mark Hammer]

On a different forum, the topic came up of hum that a particular member could simply not get rid of, no matter what guitar, what amp, or where he plugged the amp in around the house.

Which got me thinking.  I know in the "good old days", if the fridge compressor went on, or mom used the sewing machine, all audio and TV in the house was cursed with line noise.  Audio and non-audio appliances have improved in terms of line-noise generation and immunity since then.  But I'm curious and uninformed of such matters.  Have building codes for electrical wiring changed in some manner since those good old days that would have reduced the probability of line noise?  For instance, does more modern household wiring involve transformer isolation of different parts of the house, or anything like that?  Is the wiring associated with any given circuit-breaker isolated in any way from the wiring connected to other circuit-breakers?  Or is it all just one big daisy-chain, and our absence of hum and crackle is simply better designed appliances?

[vigilante397]

I'm not an electrician by any means, but I don't believe the code has changed. I have a friend that ran a recording studio in his basement and he spent a fair bit of money on isolation transformers to keep the entire basement's power separate from the rest of the house. His house was fairly new (built in 2008 I think) but the power was still just daisy chained until he intervened.

[anotherjim]

A common cause of audio noise here in the UK was our appliance AC wall plugs. New stuff was never supplied with a wall plug fitted to the cable but the wires were stripped and tinned ready for you to fit your own plugs. No matter how good you were at plug fitting, the leaded solder on the wires will cause the screw-down receptacle on the plug pins to loosen because lead flows under pressure. I can remember having to go around the house tightening them when the noise became a problem. Often discovering signs of heating in the joints. Nowadays, the plugs are pre-fitted, but they also dress the wire ends with bootlace crimps instead of solder which is far better.
House wiring has improved in some ways. The safety ground is to a proper ground stake instead of a handy water pipe (just as well as those are mostly plastic now). Also, our lighting circuits now carry a ground wire in a 3 core cable even if the fitting is plastic and I think that ground wire has some screening value.

[Ice-9]

I'm pretty sure that the UK is the only Country in the world that uses  what we call a ring mains for sockets, this was introduced many years ago when copper was very expensive (just after the war I think) and using a complete ring allowed for the use of a thinner gauge copper wire as current was shared through the return run. This can cause ground loops and by todays standards is considered a bad idea.

[davent]

Any light dimmers in the mix?
dave

[Mark Hammer]

That's an excellent question.  I'll ask the individual.

[Sooner Boomer]

You can make an easy RF probe using the high gain version of the LM386 circuit. Just attach a 6" or so piece of wire to the input pin.  For higher frequencies, you can stick an RC high-pass on the input to keep it from being swamped by lower frequencies. A cheap, easy, portable way to track down all sorts of electrical noise.

[R.G.]

Have building codes for electrical wiring changed in some manner since those good old days that would have reduced the probability of line noise? 

The electrical code changes a lot. I suspect that any improvement in noise susceptibility comes from better wiring - bigger wires, fewer outlets per wire, better distribution, more distribution transformers - than from any attempt to make the mains quieter.

But then I have the circuits-specialized EE's ingrained disdain for AC-power specialized EEs from the 1970s, when the world was young. 

For instance, does more modern household wiring involve transformer isolation of different parts of the house, or anything like that? 

No.

Is the wiring associated with any given circuit-breaker isolated in any way from the wiring connected to other circuit-breakers? 

No.

Or is it all just one big daisy-chain, and our absence of hum and crackle is simply better designed appliances?

House wiring in the USA, and I rather suspect in Canada, is a star of daisy chains. Houses have GBWs (Great Big Wires) coming into them (again, USA practice I'm most familiar with) capable of the level of power/service you paid the electrical company to install. In the USA, this is often something like 50-100A at 240Vac per house. The mains coming into the transformer supplying the house is from an intermediate transmission voltage. 13kV was once common, but I don't know what current practice is. The transformer supplying the house converts intermediate transmission voltage down to the feed to the house/building/etc. It is common, but not universal, for this to be intermediate transmission voltage 3-phase down to either 480Vac/240Vac/208Vac three phase.
Each of the three phases are usually split at the distribution (to the house) transformer into two halves of 120Vac per side. These are then supplied to the house at the specified current level from above - 50, 100, 200A or more if you pay for it. It is common for the house/building to get only one phase, the other two phases being supplied to the house/building on either side.  So you have a three phase star at the distribution transformer that is split to three houses. Each house gets two "phases" of 120vac, in the USA, and probably Canada. Don't know about 240Vac countries.

The two "phases" of 120Vac are supplied to the house breaker panel, along with a center tap on the distribution transformer. The center tap is connected to a ground rod at the distribution panel (I think) and also to a ground rod at the house/breaker box.
The distribution transformer is a star point for three or more houses/buildings depending on who set up the distribution system. In USA suburban practice, it's common for there to be one DT per three houses. Don't know in denser cities. I personally have 200A single phase DT out here in the sticks.

The breaker panel is the star point for in-house distribution. From here, the electrician wires up daisy chains to each breaker circuit. There are two "phases", remember, so the electrician tries to guess at how many lights will total about 15A, how may average outlets will use 15A or less on an average usage, which circuits need to be separated by GFIs, and so on. The name of the game for house-wiring electricians is to group uses (i.e. lighting, outlets, ovens, dryers, other built-ins, etc) to allow less than the typical 15A per breaker, and to put special high uses like 240V circuits, high power and so on, where they will be safe and under the trip per breaker. Oh, yeah - to do that with the fewest breakers, feet of wire, smallest gauge, and least call-backs for constantly-tripping breakers and house fire lawsuits.


I think... 

[amptramp]

On a different forum, the topic came up of hum that a particular member could simply not get rid of, no matter what guitar, what amp, or where he plugged the amp in around the house.

Which got me thinking.  I know in the "good old days", if the fridge compressor went on, or mom used the sewing machine, all audio and TV in the house was cursed with line noise.  Audio and non-audio appliances have improved in terms of line-noise generation and immunity since then.  But I'm curious and uninformed of such matters.  Have building codes for electrical wiring changed in some manner since those good old days that would have reduced the probability of line noise?  For instance, does more modern household wiring involve transformer isolation of different parts of the house, or anything like that?  Is the wiring associated with any given circuit-breaker isolated in any way from the wiring connected to other circuit-breakers?  Or is it all just one big daisy-chain, and our absence of hum and crackle is simply better designed appliances?

Your assumption that appliances have improved in terms of noise generation is not really all that factual.  I am on another site which has to do with FM tuners and there are a lot of modern troubles that didn't exist in the good old days.  You now have fluorescent and LED lights that have an inverter in the base that pretty much destroys FM reception.  Incandescent lights never did that unless they were hooked up to a dimmer.  Computers have switching supplies and the computer itself has been a problem ever since the original IBM PC's with a strong output from the keyboard processor at 84 MHz.  Many standalone devices have to meet FCC standards with the loophole that a computer which is embedded as part of an appliance does not - Your PC may have to meet conducted and radiated emissions but your washing machine / dryer / dishwasher / oven / microwave oven / furnace / air conditioner and all the rest of these things with embedded computers do not.

In answer to your questions about the electrical code, I grew up in a house built in 1950 with 2-pin wall outlets and a total 60 amp system.  I now live in a house with 3-pin wall outlets and a 120 amp service.  Recently, the usual service moved up to 200 amp.  Circuit breakers have supplanted fuses and there are a lot more of them - my kitchen has five outlets and they are all on separate fuses.  None of this addresses the noise problem.  The use of power bars with surge suppressors has mitigated some of the effects of voltage spikes and some power bars have EMI filtering inside and maybe that would be the solution for your friend.  But hum appears to be from radiated or conducted susceptibility or ground loops.  Does the amplifier have a ground pin?  Some of the older ones do not.  Is it just a guitar and amplifier or are there pedals that use power line power in the mix?  As a practitioner of the EMC black arts, I can say it is difficult for to diagnose anything over the internet.  You will have to go there to investigate.  Take a battery portable AM radio with you to check local noise near outlets - the AM band has been almost wiped out by noise in the past few decades.

[Rob Strand]

Which got me thinking.  I know in the "good old days", if the fridge compressor went on, or mom used the sewing machine, all audio and TV in the house was cursed with line noise.  Audio and non-audio appliances have improved in terms of line-noise generation and immunity since then.

The old sewing machines used commutated motors the noise is easily removed with caps, as was done on some cassette player motors.  Nowadays the motors are often brushless DC types; they don't produce *that* noise.

Switching noise from the fridge can be removed with a noise-suppression cap.

The reduction of noise is a two-way street:
- Reducing what gets out, and
- making the device tougher against external interference (of various sources).

The EMC regulations and experience from the noise problems from the bad-old days has made designers more aware of the problems.    However I don't believe there's any rules saying audio equipment *has to* be immune to external noise sources because it audible noise doesn't create a hazard.   Manufacturers of pro-audio equipment will protect their own interests and consciously defend against noise sources.    If you look at some on-board guitar/bass preamps they have even added parts to help reduce mobile phone interference.   However,  cheap PC speakers will not take any measures to prevent interference at all - I hear crap in my PC speakers all the time.

None of this has anything to do with house wiring.

[PRR]

Difference US and Canada is largely better details in Canadian code. Which way your main breaker throws has no effect on your audio buzz.

Residential wiring is almost never 3-phase (they charge more for that) even in the street. Nearly all breakers are now 20Amps. But history goes back a long way, and Mark's, uh, friend may own a chunk of history. The 1948 house has 15A fuses and no ground wires on interior outlets. Up until about 1920, US NEC *prohibited* connecting electricity to dirt. The oldest live installation I have seen was from 1933, transitional, one wire painted white at the ends.

However I doubt any of this relates to the related problem. Usually these things are one bad cable or some horrible electric railway the poster failed to mention.

[Rob Strand]

Residential wiring is almost never 3-phase (they charge more for that) even in the street.

We have both 3-phase and single-pahse in AU but in the last 20 to 25  years there's a lot more single-phase installs.  I suspect this has to do with cheaper installs but 25 years ago it was reported the electricity authorities wanted to control diversity by hard-wiring.

Our house has 3-phases + neutral to the street and earth stake at the house. Interestingly, as a kid I would ride the on/off point of light switches and the arc would clearly come though the stereo.   The lights and power are on different phases so the interference must be coming through as RF.   The old fridge from the 70's used to create a significant bang through the stereo (and cassette recorder).

[davent]

On a different forum, the topic came up of hum that a particular member could simply not get rid of, no matter what guitar, what amp, or where he plugged the amp in around the house.

I'll assume the issue disappears if he uses his gear elsewhere?
dave

[Mark Hammer]

The fellow just posted that, after taking stock of what may have change in the house appliances, he realized that he had his laptop and monitor situated in the kitchen right above where his gear is.  Unplugging both instantly solved the problem.