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Unread 02-06-2018, 07:17 PM
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Robot wiring vs. residential/commercial wiring

I should be mentioning this more often:

In house/building wiring, at least in the US, wire colors mean different things than they do in our robot wiring. FATALLY DIFFERENT. Learning robot wiring doesn’t qualify us to work on houses, etc.; what we learn is a helpful start, but it’s not enough. I don’t want to take time to explain this and right now you have a robot to build, but PLEASE remember this. And building voltages are much higher than in our robots in the US, and European voltages are double that, as well as in many other parts of the world.
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Unread 02-06-2018, 07:28 PM
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Thumbs up Re: Robot wiring vs. residential/commercial wiring

Thank you dear sir, for preventing the injury of many a headstrong robotics student.
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Unread 02-06-2018, 09:39 PM
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Re: Robot wiring vs. residential/commercial wiring

Quote:
Originally Posted by garyk View Post
I should be mentioning this more often:

In house/building wiring, at least in the US, wire colors mean different things than they do in our robot wiring. FATALLY DIFFERENT. Learning robot wiring doesn’t qualify us to work on houses, etc.; what we learn is a helpful start, but it’s not enough. I don’t want to take time to explain this and right now you have a robot to build, but PLEASE remember this. And building voltages are much higher than in our robots in the US, and European voltages are double that, as well as in many other parts of the world.
The robots are DC and the wiring inside your house AC. Black for the reference (or ground) and red for power is standard coloring for DC. A robot can catch fire and the wiring get really hot (enough to weld) but there is not the shock danger of AC wiring. I do not recommend it but one could grab the positive and negative terminals anywhere on the robot and the only danger is getting burned (mitigated by your instinct to avoid the heat) and there is no chance of the current travelling through your heart etc. That is not true of AC of course - it will kill you.

So be very careful, there is danger of burning and fire if you mis-wire something on your robot. But it is nothing like the AC in your home! IMHO the robot presents no serious danger to a student, parents need not be overly concerned.
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Unread 02-06-2018, 10:16 PM
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Re: Robot wiring vs. residential/commercial wiring

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Originally Posted by garyk View Post
And building voltages are much higher than in our robots in the US, and European voltages are double that, as well as in many other parts of the world.
Most houses in the US also have 240 VAC circuits, usually to an outlet in the laundry room for a dryer. Electric ovens also use 240 V, and in some cases there are additional 240 V outlets in garages/workshops for EV charging or large power tools.
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Unread 02-07-2018, 09:05 AM
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Re: Robot wiring vs. residential/commercial wiring

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Most houses in the US also have 240 VAC circuits, usually to an outlet in the laundry room for a dryer. Electric ovens also use 240 V, and in some cases there are additional 240 V outlets in garages/workshops for EV charging or large power tools.
Also, unlike FRC most houses don't have to deal with other houses ramming them at high speeds repeatedly.
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Unread 02-07-2018, 09:26 AM
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Re: Robot wiring vs. residential/commercial wiring

Is this an issue that has come up, now or in the past? That students who do electrical work on an FRC team have taken it upon themselves to do residential wiring and had some sort of accident, because they think they have training for it now?
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Unread 02-07-2018, 10:48 AM
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Re: Robot wiring vs. residential/commercial wiring

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Originally Posted by wireties View Post
So be very careful, there is danger of burning and fire if you mis-wire something on your robot. But it is nothing like the AC in your home! IMHO the robot presents no serious electrical danger to a student, parents need not be overly concerned.
Fixed that for you. Sharp edges, ramming, pneumatics, chain/sprocket, gears, etc are all quite dangerous.

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Is this an issue that has come up, now or in the past? That students who do electrical work on an FRC team have taken it upon themselves to do residential wiring and had some sort of accident, because they think they have training for it now?
+1, there must be a reason behind this thread... I wonder what it is.
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Unread 02-07-2018, 11:03 AM
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Re: Robot wiring vs. residential/commercial wiring

Something else I'd like to add: if you disassemble old appliances and electronics for repair or to salvage parts/materials from unrepairable devices (as I do), beware that unplugging does not always mean it's safe. Some devices contain high voltage capacitors that range from 50-300+ volts, which may remain charged for a while after disconnection from the power supply. In addition, cathode ray tubes can store 23,000 to 50,000 volts for over a week, even if unplugged. No, that is not a typo; CRTs in old TVs/monitors/oscilloscopes/etc. can hold twenty-three to fifty THOUSAND volts. This is where high voltage capacitors are common. They're also found often in radios and sometimes on electric motors, but hazardous voltage while unplugged is less common in modern flat panel monitors. FRC robots do not present this hazard, as maximum circuit voltage is limited to 24 V. If in doubt or if you don't feel 100% comfortable working with a device, don't.

TL;DR: Don't play with electricity. Capacitors can be dangerous. CRTs are dangerous.
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Unread 02-07-2018, 11:07 AM
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Re: Robot wiring vs. residential/commercial wiring

FRC electrical is probably a very good background for working on automobile electrical systems.

Home electrical has its own hazards and compliance codes (National Electric Code). This is no place for the unknowledgeable to be working.

I'd add that many of the US machine shops you'll encounter may have three phase power of 480V with entirely a different set of wire colors.

Green or bare wire (Bonded Ground), and white/grey (neutral) are standardized. Any other colored wire, or color taped wire is a current conductor.

Never Ever work on a live circuit.
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Unread 02-07-2018, 11:21 AM
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Re: Robot wiring vs. residential/commercial wiring

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Also, unlike FRC most houses don't have to deal with other houses ramming them at high speeds repeatedly.
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Unread 02-07-2018, 12:10 PM
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Re: Robot wiring vs. residential/commercial wiring

Interestingly the red/black color scheme for DC power only seems to be called for in NFPA 70.

NFPA79 (Electrical Standard for Industrial Machinery) calls for blue/white with blue stripe for DC conductors.
IEC calls for brown/grey or brown/blue.

Most of the sensor cables I have encountered in automation have the brown/blue convention.

FRC electrical is similar to automotive systems, except the part where most vehicles use the chassis as ground.
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Unread 02-07-2018, 12:47 PM
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Re: Robot wiring vs. residential/commercial wiring

A related issue I had many many years ago is that at 12V, it requires ~10x the current to produce the same power. Ratings of switches and contacts and such are all in terms of current. Any indication of power is only at the specified voltage! A switch which can safely control a 500W device at 120V can only control a ~50W device at 12V.
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Unread 02-07-2018, 01:26 PM
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Re: Robot wiring vs. residential/commercial wiring

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Originally Posted by GeeTwo View Post
A related issue I had many many years ago is that at 12V, it requires ~10x the current to produce the same power. Ratings of switches and contacts and such are all in terms of current. Any indication of power is only at the specified voltage! A switch which can safely control a 500W device at 120V can only control a ~50W device at 12V.
Not only this, but with switches/relays the DC rated current is always much lower as AC has a zero crossing and DC can continuously arc (contactors need a blow-off).
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Unread 02-08-2018, 12:25 PM
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Re: Robot wiring vs. residential/commercial wiring

Wiring color codes are different for different types of things. Houses use black for "hot" and white for neutral. The DC side of travel trailers also use black for 12v positive, and white for 12v negative. Automotive wiring is all over the place...you have to look up what it is you're working on, to find out what the colors mean.

Robot wiring is closer to automotive wiring than any other field, I think. But it's not the same.
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Unread 02-08-2018, 02:32 PM
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Re: Robot wiring vs. residential/commercial wiring

In industrial controls, Two wire twisted cable is commonly black and white. Except for when it is different. One convention is black is always hot (+ for DC) White is often grounded and return. (0 volts which is negative relative to plus DC). In another convention Black is negative which leaves white to be positive. In old systems you will often see these conventions mixed.

Moving on to cars, some use a positive ground. Brits are strange people some times.
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