| reply to garys_2k
Re: How to calculate the amperage of paralleled conductors??? said by garys_2k:Do you have two circuits that you need to parallel to run a single 56 A load (where the total of four conductors includes two "hots" and two neutrals, EACH being paralleled to two pairs of conductors will carry the total current)? Or, you have four circuits (four hots, four neutrals) that you will parallel to run this load? i need about 50 amps so what we are doing at the feed end is to take as many number 10 wires as we can prove out (8 or more) and connecting them to a multi-tap which is connected to a 60 amp outlet on a distrobox, then at the other end we are pulling the wires out of junction boxs close to where we need the power chopping lose from their "loads" then using more multi-taps combining them to the inlet of another distrobox and from there the lighting is connected.
the existing wiring is tinned so it's easy to work with but the junction boxes are rusted out rat bottoms that I have had to use a cold chisel and a 5 pound sledge on to get the covers off.
so far we powered up two areas wth no problems.
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| reply to whizkid3
said by whizkid3:2. There is no valid reason to parallel small conductors, aside from being too cheap to purchase the right size wire in the first place. It's a valid reason when that is all there is to work with and there is no way to replace what is there. |
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 nunyaWho is John Galt?Premium,MVM
join:2000-12-23
O Fallon, MO
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| If it's temporary, you bring in PROPERLY SIZED and RATED temporary cables. What you are doing is probably more dangerous at sea than it would be on dry land.
Ever been on a ship that's been on fire? Let me tell you firsthand - it's a whole lot of no fun. Port or not.
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If someone refers to herself / himself as a "guru", they probably aren't. |
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 ropeguruPremium
join:2001-01-25
Mechanicsville, VA | said by nunya:If it's temporary, you bring in PROPERLY SIZED and RATED temporary cables. What you are doing is probably more dangerous at sea than it would be on dry land.
Ever been on a ship that's been on fire? Let me tell you firsthand - it's a whole lot of no fun. Port or not.
While I agree, somehow I think that there probably isn't much left on the ship to burn.
"A couple of weeks and then we blow the ship up." |
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BobAccount deleted
join:2012-07-22
New Jersey Reviews:
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| reply to MatrixHDV
said by MatrixHDV:take as many number 10 wires as we can prove out
the junction boxes are rusted out rat bottoms that I have had to use a cold chisel and a 5 pound sledge on to get the covers off.
So you can't inspect the wires (you're just checking for basic continuity) and have no idea as to their condition, but you know the junction boxes are all rusted. And you're going to be putting 50 amps through them.
What could go wrong? |
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 LazManPremium
join:2003-03-26
canada | reply to MatrixHDV
Maybe it's just me, but fudging it with unknown wiring in unknown condition sounds like a lot more work and a lot more dangerous then running an appropriate chunk of Teck90 or some cam-lock cables to where you need to go...
Plus, as was mentioned, you've got to ask the right question to get the right answer... |
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 ThespisI'm not an actor, but I play one on TV.Premium
join:2004-08-03
Keller, TX | reply to MatrixHDV
Unfortunately, this kind of approach to wiring is not unusual on movie locations. That's usually nothing compared to the rigging...
In the theatre, we're a little more afraid of burning the place down.
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| reply to nunya
said by nunya:If it's temporary, you bring in PROPERLY SIZED and RATED temporary cables. i would love to do that but it is not possible given the constraints I am working under, my idea was to lay in stingers but the "safety" guy shot down that idea, now we are using the ships wiring which he has signed off on.
If you have a better idea on how to rewire a steel ship built in the 50's within three days I would love to here it.
Ever been on a ship that's been on fire? Let me tell you firsthand - it's a whole lot of no fun. Port or not. |
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| reply to ropeguru
said by ropeguru:While I agree, somehow I think that there probably isn't much left on the ship to burn. It’s pretty much steel on steel, the wiring is in steel conduit as is every junction box and everything is threadd together. |
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| reply to Bob
said by Bob:So you can't inspect the wires (you're just checking for basic continuity) and have no idea as to their condition, but you know the junction boxes are all rusted. And you're going to be putting 50 amps through them. In the boxes we have opened the wiring looks good and megs out just fine.
Hopefully nothing |
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nunyaWho is John Galt?Premium,MVM
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O Fallon, MO
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| reply to ropeguru
It isn't about the ship burning. The whole damn ship can burn and the hull will still float. It's about things like old fuel/oil, insulation, wires. It's the smoke that kills below deck, not flames.
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| reply to MatrixHDV
Does nec not apply cause you are in internatiomal waters?
Movable cables need to flex. They are made with more and finer strands. And with softer insulation. Like welding cable. Their ampacity is different from stiff thhn etc house wire.
Ampacity partly based on the area of the strands. So the general rule applies - founling the diameter quadruples the area. And ampacity.
If something goes wrong and u didnt follow code you are liable. As is anyome else who helped you. And if you know code and still dont follow it you are liable for treble damages |
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| said by flex :Does nec not apply cause you are in internatiomal waters? Not really once off shore it will only be maybe a half mile out.
None the less after glossing over the code last night it appears we would be in compliance under 90.4 as the safety guy is an "insurance inspector" makinghim the authority having jurisdiction and he signed off on it.
Movable cables need to flex. They are made with more and finer strands. And with softer insulation. Like welding cable. Their ampacity is different from stiff thhn etc house wire.
Stuff like this.
founling the diameter quadruples the area. |
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 dandemanPremium,MVM
join:2001-12-05
Chapel Hill, NC
 ·AT&T Southeast
2 edits | The problem will paralleling conductors is that in practical application, there's no assurance that the current will be divided evenly..
Unless you have engineering experience in very low impedance systems it will be hard to see why..
Same gauge, same length cables will have small differences in the resistance, as my work has involved, down in the micro-ohm range. If one length of cable turns out to be for example 400 micro-ohms, and another cable 100 micro-ohms, then ohms law says the 100 micro-ohm cable will carry the by ratio the brunt of the current.. Connector crimping and other small mechanical connection diffierences can contribute to these small variations. Even if you start out, evenly matched, corrosion and other degradation over time can cause differences to develop..
The only way to do this safely for fire protection would be to protect each cable with it's own breaker rated for the individual conductor, then if the current divide developed enough difference and started overloading one of the cables that c/b would trip.. then of course the load would shift to the other cables, likely causing progressive tripping of all the breakers and dumping the load..
I posted this just to explain the failure mechanism that could lead to conductor overload and fire only, and not as a justification or rationale to violate code.
Of course if it's an off shore, special application beyond what prescriptive code practices cover, then do, or get your own professional engineer to review it, sign off with his stamp on it rather than ask for opinions here......
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| reply to MatrixHDV
Thanks. I meant
doubling the diameter of a circle quadruples its area.
Please keep your ears open to the folks who from theory and experience are telling you not to do this. If u do it anyway be prepRed for worst case of redhot melting dripping bare wire. and to lowells - tie in and see god.
Plan b might be to suggest led lights instead of hmi |
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 cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7 | reply to MatrixHDV
said by MatrixHDV:None the less after glossing over the code last night it appears we would be in compliance under 90.4 as the safety guy is an "insurance inspector" makinghim the authority having jurisdiction and he signed off on it.
So you're using the NEC to try to justify that it's ok, but earlier you said that the work doesn't fall under the NEC.
Also, AHJ doesn't just work that way where if an "insurance inspector" says it's ok then everything is fine and dandy. For safety issues, usually AHJ is an individual that is granted authority by statue. E.g. electrical inspector, fire marshal, etc. |
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BobAccount deleted
join:2012-07-22
New Jersey | reply to dandeman
I not sure he knows if the cables are really the same length or not. |
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 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6
·SONIC.NET
1 edit | Probably not, but there are a number of ways to determine ahead of time whether the individual wires selected for bundling have the same electrical characteristics.
That wouldwouldn't solve any code compliance issues but it does address safety concerns.
Other things that can be done to improve safety are using significant margins (e.g. calculated current carrying capacity more then 300% of design load) and 200% load test prior to the actual event (if possible doing thermal imaging of conduits and junction boxes).
Edit: oops, would => wouldn't
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| reply to MatrixHDV
also fyi
standard ampacity is for single wires in open air at standard room temperature. if the wires are in the hot sun and/or hot ambient and/or confined in conduit and/or bundled, each of those conditions needs a derating affect. the code book will specify. |
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| reply to cdru
said by cdru:said by MatrixHDV:None the less after glossing over the code last night it appears we would be in compliance under 90.4 as the safety guy is an "insurance inspector" makinghim the authority having jurisdiction and he signed off on it.
So you're using the NEC to try to justify that it's ok, but earlier you said that the work doesn't fall under the NEC. Na just pointing out something I never realized is possible, you see the majority of my work connects to services that are already "approved" or we bring our own power.
Though I do believe if it was connected to shore power then the NEC would apply and what we are doing would not be permitted as the local electrical inspection department would not go along.
Now I don’t get involved in that type of work as it is normally handled by the house electrician who works with the inspection department. |
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