Low Voltage Distribution at Home

markad1

Bruthal wrote: »

Perhaps a quote of the poster in the reply to help them see.

ok

Bruthal

frankmul wrote: »

Some thing along these lines, https://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

They seem a bit overly simplistic in calculations in that. One thing is right though, the skin resistance is quickly reduced as voltage increases. Far more severe shocks are inflicted with 230v than 110, and again when it steps to 400v.

It would be some shock to receive 2 amps though, even from 1000 volts, which id say would be unlikely. That would be heading for destruction of body parts. Got a nice one from 2.5kv before. Horrendous whack. Tried a moving solenoid 1000v esb test lamps on it after it happened. Instantly ended its useful life.

frankmul

Bruthal wrote: »

They seem a bit overly simplistic in calculations in that. One thing is right though, the skin resistance is quickly reduced as voltage increases. Far more severe shocks are inflicted with 230v than 110, and again when it steps to 400v.

It would be some shock to receive 2 amps though, even from 1000 volts, which id say would be unlikely. That would be heading for destruction of body parts. Got a nice one from 2.5kv before. Horrendous whack. Tried a moving solenoid 1000v esb test lamps on it after it happened. Instantly ended its useful life.

Where did you get 2.5 kv from. Discharge lighting?

Bruthal

frankmul wrote: »

Where did you get 2.5 kv from. Discharge lighting?

It was a commercial microwave oven transformer. Two magnetrons in microwave. It was only giving half power so the procedure was to disconnect one and heat some water to find which was the faulty one by elimination.

Managed to hit hand off the spade connection and other hand was on the steel frame of the microwave wall bracket. Such a whack like nothing ever before or since.

frankmul

Bruthal wrote: »

It was a commercial microwave oven transformer. Two magnetrons in microwave. It was only giving half power so the procedure was to disconnect one and heat some water to find which was the faulty one by elimination.

Managed to hit hand off the spade connection and other hand was on the steel frame of the microwave wall bracket. Such a whack like nothing ever before or since.

Ouch!

Bruthal

frankmul wrote: »

Ouch!

It was horrendous, only in contact for fraction of second, after which hands went involuntarily down to sides, with fingers clenched. Was like that for a good few seconds. 20 years ago now.

Chet T16

Bruthal wrote: »

It was a commercial microwave oven transformer. Two magnetrons in microwave. It was only giving half power so the procedure was to disconnect one and heat some water to find which was the faulty one by elimination.

Managed to hit hand off the spade connection and other hand was on the steel frame of the microwave wall bracket. Such a whack like nothing ever before or since.

One hand in the pocket!

I've been looking at this problem for a while. I'd run an entire house on DC if I could.
Given a house with a DC supply. Last time I dropped the issue I speculated that after the first two rooms the expense involved in low loss cabling compared to the elevated efficiency losses of inverters/transformers outweighs the overall transportability of AC.
Seems to me to run AC from a DC source back to a device local DC supply is the most cost effective.
You may find otherwise given that you are only pulling down mA.

Bruthal

Chet T16 wrote: »

One hand in the pocket!

Time machine?

Chet T16

Bruthal wrote: »

Time machine?

Future reference although i suspect you knew it already and definitely stick to it now

Chet T16

Sir Liamalot wrote: »

I've been looking at this problem for a while. I'd run an entire house on DC if I could.
Given a house with a DC supply. Last time I dropped the issue I speculated that after the first two rooms the expense involved in low loss cabling compared to the elevated efficiency losses of inverters/transformers outweighs the overall transportability of AC.
Seems to me to run AC from a DC source back to a device local DC supply is the most cost effective.
You may find otherwise given that you are only pulling down mA.

From reading about cat5 it looks like 24v DC at 1A is well within spec using a single wire, i'll be using two.

My sensor boards will use minimal power, the radiator valves would be my only concern but even then i don't see an issue.

Bruthal

Chet T16 wrote: »

Future reference although i suspect you knew it already and definitely stick to it now

Well there was no need for a hand in pocket while working on them microwaves. Cable with spade connector safely tied up, and no hands near the microwave except to press the start button on the front panel.

My problem was I left the spade end hanging out, and brushed off it when I went to scratch the head or something.

After that it was cover the cable end and tie it up properly.

Stranded cable is more appropriate for DC.

Bruthal

Sir Liamalot wrote: »

Stranded cable is more appropriate for DC.

Any reasons you're thinking of?

Its more flexible, better to terminate, better against vibration, but they can apply in ac or dc, although heavy DC currents are prevalent for engine starting etc where vibration resistance is needed.

Current capacity in dc would depend more purely on CSA than in ac probably, apart from needing good terminations.

tomdempsey200

better connections with stranded or flexible I suppose

Bruthal

tomdempsey200 wrote: »

better connections with stranded or flexible I suppose

Yes but that would apply to both AC and DC

CSA is significant. DC only travels the surface of the conductor unlike AC which vibrates along the whole core. Always fighting voltage drop on elaborate DC systems.
I'm changing tack and currently looking at DC for batteries and AC coupling for loads on demand as a more more feasible way to reduce system losses.

Cat V comes in solid and stranded core...only learned recently, I always ended up with solid core before on jobs. Can't abide the stuff myself, it's good stuff for an install as data cable with Cat V compatible equipment (pointless as as DMX to Cat V, power etc...). It's kinda throw away cable though if you're doing turnovers...too flimsy. I'd often use 7 core automotive trailer cable with preference if I need that many lines.

brightspark

Sir Liamalot wrote: »

CSA is significant. DC only travels the surface of the conductor unlike AC which vibrates along the whole core.

Any source for that?

My understanding was that Eddy currents caused the skin effect in AC systems, the effect increasing with the frequency.

2011

Sir Liamalot wrote: »

CSA is significant.

With AC and DC, yes.

DC only travels the surface of the conductor unlike AC which vibrates along the whole core.

I assume that you are talking about the Skin Effect?

It is actually the other way around.
With AC the electric current flows mainly at the outer edges of the conductor (or skin).
The skin effect causes the effective resistance of the conductor to increase.
This effect increases as the frequency increases.
This reduces the effective cross sectional area of the conductor.

I think that you are over thinking this.
To reduce volt drop use a cable with a larger cross sectional area.

2011

2011 wrote: »

I think that you are over thinking this.

haha..yeah usually! Not likely to stop soon either...don't worry I do understand the inherent values in KISS, I said looking. It'll be years before I make my mind up.
The price of copper is the limiting factor in conductor size for me in terms of home distribution.

Thanks for the correction, I was convinced contrary, it corresponded neatly as my wiring applications are a combination of high flexibility, vibration requirements; automotive, small scale campervan off grid electrics, solar PV, wind turbines and rolling in and out of gigs...seeing these (mostly) DC sources were always on stranded cables it reinforced my misinterpretation . I read of the skin effect, can't remember where and guess I confused the context.

tomdempsey200

Sir Liamalot wrote: »

CSA is significant. DC only travels the surface of the conductor unlike AC which vibrates along the whole core. Always fighting voltage drop on elaborate DC systems.

is the current carrying capacity not the same for ac/dc

It is but substituting the inverter -> transformer losses in preference for voltage drop and regulator losses gets real expensive.

I have a localised DC setup works great without an inverter, about 40% more efficient because it's so close to the batteries. Doesn't scale up so well.

Bruthal

Sir Liamalot wrote: »

I was convinced contrary.

I was wondering had you them mixed up when seen the DC is better in stranded,,, post alright.

Bruthal

tomdempsey200 wrote: »

is the current carrying capacity not the same for ac/dc

The skin effect in ac is why 2 half size conductors in parallel have less losses than one larger one. Although a bigger cable also can't dissipate heat as well either since doubling CSA doesn't double the surface area , so 2 smaller cables in DC might also be better than 1 larger one, although DC applications wouldn't need them really. But in ac the skin effect alone would mean the above is true.

I find that using 2 conductors often has a contact resistance imbalance and afterwards doesn't fully equalise the loading. In terms of running two 1.5mm cores where what's needed is a 3mm core.

tomdempsey200

it's not allowable anyhow to split up final circuits into 2 cores

2011

tomdempsey200 wrote: »

it's not allowable anyhow to split up final circuits into 2 cores

Do you mean feed a load with cables connected in parallel?
What about a ring socket circuit?

tomdempsey200

2011 wrote: »

Do you mean feed a load with cables connected in parallel?
What about a ring socket circuit?

it's not considered a parallel circuit for the purpose of wiring rules

although it is a form of parallel wiring

rules: 555.1.3

Bruthal

tomdempsey200 wrote: »

it's not allowable anyhow to split up final circuits into 2 cores

It's pointless anyway with small conductors.

As a rule of thumb AC priority is heat dissipation whereas DC priority is voltage drop. Making DC conductors a lot more substantial. I use 100A cable to deliver 10ADC 7 meters away @ 12V.