Grounding vs. Bonding

I recently attended an online presentation from EC&M and Mike Holt regarding grounding and bonding. Within the first five minutes, I had two misconceptions shattered, and apparently I am not alone. My understanding of grounding came from forty years on the management side of electrical construction. What I have seen on electrical drawings, the information from electrical engineers and the demands of electrical inspectors have shaped my understanding of this subject.

As embarrassing as this may be, here are what my misconceptions were.

First, I thought electricity wants to go to ground. This is not true. The electrons in an electrical system are not trying to get to the earth (ground), they are trying to return to the source, usually a transformer. If the earth is the best return path, the electrons will use it. A very personal example happened to me in high school. I was washing the car, getting ready for a date. I was barefoot, standing on wet grass, and bent over to pick up an extension cord terminated in a 4S box with a duplex receptacle and a raised cover. There was no ground wire in the extension cord. The shock made me straighten out and fall backwards, pulling the box out of my hand, and most likely saving my life. The fault current in the box was looking for a return path to it’s source. Since there was no ground path through the extension cord, it found me, barefoot in wet grass, and returned to it’s source through me and the ground.

Second, as noted above, fault current is not trying to get to the earth. This is what I thought ground rods, counterpoise, rebar and metallic pipe grounds were for, and they are not. These systems are for induced currents, such as from lightning. When lightning strikes near a structure, it’s magnetic field induces current in the wiring systems of the structure. It is this current that needs to find it’s way to the earth.

Click on comment and let me know what you think of this. CLICK HERE to see the presentation from EC&M and Mike Holt.

Advertisements

A Primer For Electrical Estimating Software, Part 4

Function 3, Summary – Most of the current estimating programs have an audit trail, or takeoff report. This report displays the full detail of every item you input, and can get rather long. Even a small project could have a twenty page takeoff report. To shorten this up, the summary (also known as an extension) report can be created. This function condenses the takeoff into a report that has just one line for each item in the takeoff. If you have taken off 1/2″ EMT in twenty different places, it will be totaled up and shown on one line in this report.

This format makes it much easier to review and analyze your estimate. This is the perfect place to look for problems, such as:

• Typos, like set screw instead of compression EMT fittings
• Missing takeoff, like “I thought there was a manhole”
• Large purchases – Send them out for better pricing
• Big labor items – Should they be factored
• Missing prices and labor

Some of the available estimating systems allow editing in the summary, which can be very handy.

Function 4, Recapitulation – Up to this point, the software has only been dealing with material dollars and labor hours. The recapitulation (recap for short) is where everything else is added. This includes:

• Quotes (such as light fixtures)
• Labor dollars (converted from the labor hours)
• Subcontractors (such as communications)
• Rentals (such as a crane)
• Indirect Job Expenses (such as project management)
• Direct Job Expenses (such as expendable tools)
• Markups (tax, overhead, profit and bonds)

Some of the programs also allow you to create multiple bids in recap, such as Base Bid and Alternate 1.

When all of the preceding items are input, the system will either display your bid totals, allow you to print out bid total reports, or both. Since all calculations are instant, you should have plenty of time to fine tune the recap to be as competitive as possible. You can make as many changes as you want, and the computer will recalculate each one immediately. The software makes bid day much less stressful then it is with pen and paper systems.

Conclusion – This series of posts have been a review of the basic functions of electrical estimating software. Each of the different systems will have their own set of features, and each of the vendor may also have multiple versions of their software, such as basic and advanced. It is difficult to make a decision when buying electrical estimating software, and it will take some time to do it right. I suggest making a list of the features that appeal to you, and weight each feature’s importance. Compare the various software offerings to your list, and let the list evolve as you learn. Many of the software vendors will allow you to take a test drive of their systems at no charge. Take enough time to become familiar with the software, and do not hesitate to call the vendor with question.

As usual, if you have any questions, click the comment button or send me an email. I am interested in discussing any electrical estimating system you may have questions about.