GOAL Electrical And Mechanical Construction

Dangers of Electrical Shock

From the NIOSH Electrical Safety Manual

RULE #1: TURN IT OFF FIRST!

The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current passes through the body. For example, 1/10 of an ampere (amp) of electricity going through the body for just 2 seconds is enough to cause death.

The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less than 10 milliamperes (milliamps or mA). Currents above 10mA can paralyze or “freeze” muscles. When this “freezing” happens, a person is no longer able to release a tool, wire, or other object.

In fact, the electrified object may be held even more tightly, resulting in longer exposure to the shocking current. For this reason, handheld tools that give a shock can be very dangerous. If you can’t let go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that control breathing cannot move). You stop breathing for a period of time.

People have stopped breathing when shocked with currents from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis. Currents greater than 75 mA cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition will cause death within a few minutes unless a special device called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.

The table shows what usually happens for a range of currents (lasting one second) at typical household voltages. Longer exposure times increase the danger to the shock victim. For example, a current of 100 mA applied for 3 seconds is as dangerous as a current of 900 mA applied for a fraction of a second (0.03 seconds).

The muscle structure of the person also makes a difference. People with less muscle tissue are typically affected at lower current levels. Even low voltages can be extremely dangerous because the degree of injury depends not only on the amount of current but also on the length of time the body is in contact with the circuit.

What Should I Do If a Co-Worker Is Shocked or Burned by Electricity?

Shut off the electrical current immediately if the victim is still in contact with the energized circuit. While you do this, have someone else call for help. If you cannot get to the switchgear quickly, pry the victim from the circuit with something that does not conduct electricity such as dry wood.

Do not touch the victim yourself if he or she is still in contact with an energized electrical circuit! You do not want to be a victim too, and electricity will pass from the victim right into YOU if you’re not careful.

Do not leave the victim unless there is absolutely no other option. You should stay with the victim while Emergency Medical Services (EMS) is contacted. The caller should come back to you afterwards to verify that the call was made. If the victim is not breathing, does not have a heartbeat, or is badly injured, quick response by a team of emergency medical technicians (EMT’s) or paramedics gives the best chance for survival.

To download your copy of the Manual On Electrical Safety, see our “Electrical Safety” Page or just go HERE

I have learned that when making Three-Phase Motor Connections, The easiest way to remember the various configurations is by using the very simple “Rule Of Eleven”.

It goes without saying that you should ensure that ALL power sources are off and Locked-Out…

A typical three phase motor has 9 wires to be connected, typically numbered T1 - T9.

To Make Low-Voltage Connections, proceed as follows:
*All Connections have THREE wires connected together.

1. Connect 4, 5 and 6 together. (three wires)
2. Connect 7 and 1 together. THINK OF THIS AS 71. Connect one phase here (three wires)
3. Add 11 to 71 (71 + 11 = 82)
4. Therefore 8 and 2 are connected together. THINK OF THIS AS 82. Connect one phase here. (three wires)
5. Add 11 to 82 (82 + 11 = 93)
6. Therefore 9 and 3 are connected together. THINK OF THIS AS 93. Connect the last phase here. (three wires)

To Make High Voltage Connections, proceed as follows:
*All Connections have TWO wires connected together.

1. Connect one phase to 1. (two wires)
2. Connect one phase to 2. (two wires)
3. Connect one phase to 3. (two wires)
4. Connect 4 and 7 together. THINK OF THIS AS 47. (two wires)
5. Add 11 to 47 ( 47 + 11 = 58 ).
6. Therefore 5 and 8 are connected together. THINK OF THIS AS 58. ( two wires )
7. Add 11 to 58 ( 58 + 11 = 69 )

Therefore 6 and 9 are connected together. THINK OF THIS AS 69. ( two wires )

It’s as simple as that! Of course, don’t forget to bump the motor, check the rotation, and switch phases if needed to get the proper phasing before starting up!

The widespread usage of PVC Conduit has forced electricians to come up with some pretty novel ideas for dealing with the peculiarities of this material. Below are some of the A-list tips from our forum. I think you will find them very useful!

First of all, when PVC Conduit is bendable, it is HOT. Whether you are using a hot-box, torch, or whatever, you need to have a bucket of water on hand. Now, if you are a genius, you will stop at the local dollar store, and get a pair of oven gloves!

Soak them in the bucket of water, and when you pull the pipe out of the heater, slip them on and you will be able to form and cool the pipe in one operation…painlessly!

Many times in the field we find that we need to make a number of identical radius bends for duct banks, etc. The best way I have found to do this is by making an EMT template and checking it first (any size EMT will do), and using that for a production gauge. Every one of your bends will be perfect, and identical.

When making PVC to RIGID Transitions, we have all had terminal adaptors and female adaptors slip, fall out, etc. I mean there just isn’t enough Meat on the fitting to make a quality joint, right? And, they ALWAYS leak! Here’s the solution: Omit the fitting entirely!

Make sure you have primer and good cement on hand. Prime the bell end of your PVC, and Glue the nipple or elbow directly into the bell- Threads and all. Use LOTS of glue! Then, for an added measure of “cheap insurance”, take some quick setting clear adhesive silicone, and caulk the shoulder of the PVC where it meets the rigid. Voila! A super strong transition that you can pull with confidence.

Another thing we have all had happen is broken underground pipes. A very quick and high quality way to repair the damage is by correctly splicing in a new piece of conduit.

First, excavate and clean up around the break to expose enough pipe to get it back in line as best you can. The larger the conduit, the more you will have to dig out. Then, cut back and square up the ragged ends, deburr, and clean the ends thoroughly.

Measure and cut your splice from a full conduit that has a bell end intact about a 1/4-1/2 inch shorter that the actual span. Then, sacrifice a stick of conduit (if you have no scraps with bell ends), and cut the bell off cleanly just at the taper to make a slip fitting.

With smaller conduits (1″ or less) you may be able to use a standard coupling and just “bow” the ends together, but larger conduit won’t allow this.

You can also remove the ridge from the inside of a standard coupling, but that’s a LOT of work, and they are often very tight and difficult to work with, so I don’t recommend this.

Lightly soap the inside of your slip fitting with wire lube or dish soap (don’t use grease or oil), and slide onto the blank end of your splice pipe. Make a mark at half the width of the slip fitting on the broken pipe adjacent to where the slip fitting will go so that you can get it centered.

Prime and glue up the bell end of the splice to one end of the break, and, working quickly, slide the slip fitting over the other end to the mark you made previously. You may need to tap the fitting with a block and hammer to get it to slide, but it will go.

Wash off the soap residue from around the fitting with water and dry. Use a high-quality clear adhesive silicone to seal the shoulder of the fitting to the pipe.

Congratulations…You have just saved yourself thousands of dollars in excavation and lost time!

For more great tips like this one, be sure and sign up for our FREE newsletter using the form at the top right of this page!