The basics
What it is
Insulating bucket trucks and insulating digger derricks have a fiberglass section in the boom. The maker tests that section and rates it for a line voltage. The rating is stamped on the ID plate, next to the category. A dielectric test puts a known test voltage across the fiberglass and reads how much current leaks through. Clean, dry, sound fiberglass leaks very little. Dirty, wet or damaged fiberglass leaks more, and past a set limit the unit fails.
There are two kinds of test. The qualification test sets the rating. It is run with an AC test set by the maker or the installer, and it comes back around when a fiberglass boom section is replaced or modified. The periodic test is the one on your calendar. It is also called the annual or maintenance test, and it can be run with AC or DC equipment, one or the other, not both. The figures on this page are the DC ones.
The point
Why it matters
You cannot see it. Fiberglass that will hold off 46 kV and fiberglass that will not can look the same from the ground. What breaks it down is usually dirt or moisture on or inside the boom, a cracked or gouged section, contaminated hydraulic oil, or a hose or leveling rod that was changed and altered what crosses the insulating section.
Know what the insulation is for, too. On most units the boom is a second layer behind PPE and work procedures. Only a Category A unit worked with barehand procedures counts as primary protection. And the rating is the phase to phase voltage of the line. A 46 kV unit does not go on a 69 kV system, even though the phase to ground voltage of that system is under 46 kV.
No periodic test in the last 12 months? Do not treat it as insulating.
Who it is for
Who needs it
If your boom is supposed to keep you off a line, somebody has to prove it on schedule.
- Utility contractors and line crews
- Municipal and co-op utility fleets
- Line-clearance tree crews with insulated buckets
- Telecom and cable crews with insulated units
- Owners of insulating digger derricks
- Rental and sales yards, before a unit goes out
- Anyone who bought a used unit with no test history
Look at the ID plate. If it does not say the unit is insulating, there is no dielectric rating to test. The structural inspection still applies, and that is a different job. See ANSI aerial lift and crane inspections.
The test sheet
What gets checked
DC periodic test, upper boom, ratings to 138 kV.
| Rated for (phase to phase) | Applies to | Test voltage, DC | Hold time | Max leakage |
|---|---|---|---|---|
| 46 kV and below | Category A and B | 56 kV | 3 minutes | 28 microamps |
| 46 kV and below | Category C and insulating digger derricks | 56 kV | 3 minutes | 56 microamps |
| 69 kV | Category A and B | 84 kV | 3 minutes | 42 microamps |
| 138 kV | Category A and B | 168 kV | 3 minutes | 84 microamps |
Flashover, or leakage over the limit, is a fail. These numbers come from published manufacturer DC test procedures and the periodic test table in A92.2, and they assume a DC set that reads output current. A set that reads return current has its own procedure. Your owner's manual and the current edition of A92.2 are the last word, and they win over anything on this page.
Before the voltage goes on
- Clean and inspect the boom, inside and out. Dirt, moisture and nests inside the boom are what fail units, and a nest in a live test is a fire.
- Dry, roped-off work area. Unit grounded and test jumpers set the way the procedure calls for.
- Boom set in the position the procedure calls for, and that position written down. Position moves the readings, so it is repeated each year.
The test itself
- Voltage brought up gradually to the test value and held for the full time. Leakage read and recorded.
- Lower boom insert or chassis insulating system, if the unit has one. It has no rating, only a test requirement, and the same method applies.
- Insulating liner, if one is fitted. It gets an annual test too. It insulates by thickness, so gouges and cuts can fail it.
- High-resistance upper control handles, on units that have them, tested annually or after work that could affect them.
Worth doing at the same visit
- Hydraulic oil check. Maker engineers point to new oil above 25 kV and used oil above 15 kV when tested to ASTM D877. Milky or dark oil is a flag.
- Compare this year's leakage to last year's. A climb over time says the fiberglass, a hose or a leveling rod needs a look before it fails.
- Rubber gloves, blankets, sleeves and hot sticks can ride along. They run on their own clock, listed below.
Intervals
How often
The standards give a floor. Heavy use near lines, or a bad month, is a reason to test sooner.
- Every 12 monthsUpper boom, liner, lower insert and upper controls. Maker engineers describe the periodic test as annual for most classes of machine, shorter if your own policy says so.
- After repairs to the insulating sectionReplacing hoses, leveling rods or anything else that crosses the insulating section, or replacing an insulating part, means a periodic test before the unit goes back to work.
- When a boom section is replaced or modifiedThat needs a new qualification test with an AC set, done by qualified service people. The old one is no longer valid.
- When something looks or feels offContaminated or damaged fiberglass, or an unplanned touch to an energized line. A test tells you whether the insulation is still there.
- Category A in barehand workTighter schedule than the annual. Follow the manual and the current A92.2 for your unit.
- Rubber gear and hot sticksGloves every 6 months and blankets and sleeves every 12, under OSHA 1910.137. Line hose and covers when the insulating value is in doubt and after repair. Live-line tools used for primary protection come out of service every 2 years for exam and test.
The rulebook
Standards the work follows
We test to the standard and your maker's procedure. We do not make up numbers.
- ANSI/SAIA A92.2Vehicle-Mounted Elevating and Rotating Aerial Devices. Sets the categories, the qualification and periodic electrical tests, and the owner's inspection and record duties.Use the current edition and the maker's procedure for your unit.
- ANSI/ASSP A10.31Digger derricks. The matching standard for insulating derricks and their tests.
- OSHA 1910.67 and 1926.453Aerial lifts. Both point to ANSI A92.2 for design, and field modifications have to be certified in writing by the maker or an equivalent entity.
- OSHA 1910.269(p) and 1926.959Mechanical equipment near energized lines, including how the insulated part of an aerial lift is treated. Part of 1926 Subpart V for construction work.
- OSHA 1910.269(j) and 1926.957Live-line tools: daily wipe and inspection, and removal from service for exam and test every 2 years when used for primary protection.
- OSHA 1910.137Test intervals for rubber insulating gloves, blankets and sleeves.
- ASTM F711 and IEEE 516F711 covers fiberglass rod and tube for live-line tools. OSHA points to IEEE 516 for tool care and in-service testing.
- ASTM D877Dielectric breakdown voltage of insulating oil, used for the hydraulic oil check.
The route
How a job goes with Convoy
One call covers it. We stay on the job until the paperwork is in your hands.
Send the plate info
Unit numbers, and for each one the category and qualification voltage from the ID plate. The date of the last test too, if you have it.
We schedule the work
A qualified technician with the right test equipment comes to the truck. Bundled by yard, so one visit covers every unit there.
Test day
Inspect, clean, test, read and record. Rain or a wet boom can stop a test, and a good crew reschedules before it forces one.
Results and records
Pass or fail with the numbers. On a fail the crew says why, and we handle the fix and the retest. Your due dates move forward.
The paperwork
What you get back
Written, dated, signed. If it is not on paper, it did not happen.
- Unit number, serial number, category and qualification voltage from the plate
- Date, who ran the test, and the test type (AC or DC)
- Test voltage, hold time and the leakage reading for the upper boom
- Boom position, so next year's test matches this one
- Separate readings for the lower insert, liner and upper controls if the unit has them
- The test equipment used and its calibration date
- Pass or fail. On a fail, the cause and what was done about it
- Your due date list, updated
The 2021 edition of A92.2 expects whoever runs the periodic electrical test to document it and give the owner a certified report on request. Ask for it. Plan on keeping reports at least five years, longer if a rule or a customer says so.
Straight answers
Questions we get
Not here? Ask. We will tell you if we do not know.
Can you test with a DC set?
Yes. For the periodic test A92.2 allows AC or DC, and one meets the requirement. You do not need both. The DC figures are in the table above. The qualification test is the one that needs AC.
Does a pass mean I can work any line?
No. The qualification voltage on the plate is the most you can work, as a phase to phase system voltage. Boom insulation is a second layer behind PPE and work procedures, except for Category A units worked with barehand procedures.
The jib is fiberglass. Is it insulating?
Not unless it is rated and tested for the voltage. Treat a jib as conductive otherwise, and use link sticks or insulating jib inserts when handling energized conductors.
What happens if the unit fails?
It is not an insulating unit until it passes. The crew finds the cause. Often it is dirt, moisture, oil or a hose, and a clean and retest fixes it. If the fiberglass itself is bad, that is a repair or a new boom section, and a new qualification test after.
Is this the same as the ANSI inspection?
No. The periodic inspection looks at structure, pins, hydraulics and controls. The electrical test is its own item in that inspection, so most owners book them for the same visit. See ANSI aerial lift and crane inspections.
Need dielectric testing? Get a quote.
Tell us what you run and where it sits. We come back with a price and a plan. A rough list is fine.