Prysmian MV Cable Inspection: A 4-Step Checklist Before Energizing

If you're about to energize a Prysmian MV cable run—whether it's a 15 kV feeder for a substation or a 35 kV circuit to a large motor—stop and run through this checklist first. I'm a quality inspector for medium-voltage cable installations. I review them before they go live, roughly 120 a year. In our Q1 2024 audit, I rejected 14% of first-time MV installations for problems that showed up in one of these checks. Most were fixable. Some were expensive.

I don't say that to scare you. I say it because the checklist below is the one I actually use when I'm standing in a trench or a switchgear room. It's not a substitute for the manufacturer's installation manual. It's the four checks that catch the most commissioning failures.

Who this checklist is for

This is for electrical contractors, plant engineers, and quality reps who sign off on new Prysmian MV cable work. If you're doing a 600 V feeder, you can use parts of it. But the voltage, cleat, and testing details are tuned for medium voltage—roughly 5 kV to 35 kV.

The short version: verify the cable, check the cleats, run a voltage drop calculator, and test continuity with a multimeter. The fourth step is the one most people are tempted to skip.

Step 1: Verify the Prysmian MV cable specs before you pull anything

Read the cable print. It should include the manufacturer, voltage rating, conductor size, insulation material, and a standard reference such as UL, ICEA, or IEC. For a Prysmian MV cable, the voltage class and conductor gauge are printed on the jacket. They need to match the purchase order and the drawings.

I know this sounds too basic to be a step. But I once found a 5 kV cable sitting in a trench where the design required 15 kV. The markings had been misread during unloading, and nobody checked. The cable was already pulled. That was a costly fix.

Step 2: Torque Prysmian cable cleats to spec—not 'hand tight'

Cable cleats are not a decoration. They hold the cable in place during a short-circuit, when the magnetic forces can be enormous. Prysmian cable cleats are tested to IEC 61914 for short-circuit withstand—but that test assumes the cleat is installed correctly.

Check three things:

• The cleat size matches the cable's outer diameter. A loose fit means no real restraint.
• The spacing follows the design. The maximum spacing is usually in the cleat data sheet or the project specification.
• The bolts are torqued to the value in the data sheet. Not 'hand tight.' Not 'a bit more to be safe.' The specified value.

I had a project where the contractor used the right Prysmian cable cleats and the right spacing, but left the bolts only finger-tight. The logic was they didn't want to crush the cable. Fair enough. But under-torquing is just as bad. A loose cleat lets the cable move under fault current, which can damage the termination or the jacket. That incident cost us a $22,000 redo and delayed the substation by two weeks.

Think of a cable cleat the same way you'd think of a blood pressure cuff on a patient. If the cuff is too loose, the reading is meaningless. If the cleat is too loose, the protection is meaningless. Use the right size and the right pressure.

Step 3: Run a voltage drop calculator before you pull the cable

Voltage drop is usually an afterthought for short MV runs—and it can be the whole problem on a long one. I can only speak to land-based industrial and utility work; if you're doing a submarine link or a tunnel with high ambient temperatures, you'll need more detailed modeling. But for normal installations, the rule is simple: run a voltage drop calculator using the actual conductor length and the actual load current.

For a three-phase circuit, the basic formula is:

VD = 1.732 × I × L × R / 1000

• I = full load current in amps
• L = one-way conductor length in feet
• R = conductor resistance in ohms per thousand feet. Use the manufacturer's AC data if you can; NEC Chapter 9, Table 8 gives DC values, which are close enough for a screening calculation.

The NEC target is a maximum of 3% voltage drop for a branch circuit and 5% total for feeders plus branch circuits, per the informational notes to NEC 210.19(A) and 215.2(A)(1). For MV cables, resistance is low, but with a 1,500 ft run and a 300 hp motor, you can still see the number move. The calculator needs the actual route length, not the straight-line distance on the drawing.

I used to be casual about this until we had a pump that wouldn't start. The feeder was designed at 420 ft, but the field route was 590 ft because it had to go around a building. The motor's minimum voltage requirement was just above what the circuit delivered. If we'd run a voltage drop calculator with the actual length, we would have upsized the conductor or moved the transformer. That was the third time something like that happened. (Should mention: we finally created a formal voltage drop verification process in 2022.)

Step 4: How to Use a Multimeter for a Basic Continuity Check

If you've been searching for 'how to use multimeter' on a jobsite, here's the version that matters for MV cable. This is not a complete guide to every function; it's the part that catches the most commissioning problems.

This is the step people skip because the cable is new. The phrase I hear is, 'What are the odds it's broken?' Well, the odds are not zero. In 2023, a newly pulled 15 kV cable had a damaged conductor where it passed under a road. The damage wasn't visible. A multimeter continuity check caught it.

1. Disconnect and isolate the cable at both ends. Ground it first, and keep it grounded while you work.
2. Discharge the cable. MV cable can hold a charge even after the breaker is opened.
3. Set your multimeter to the continuity setting or the lowest ohms range.
4. Touch the two leads together. You should see near-zero ohms. That confirms the leads and the meter are working.
5. Connect one lead to a conductor at one end and the other lead to the same conductor at the other end. A continuous conductor shows near-zero ohms.
6. Check between conductors and between each conductor and shield/ground. You should get an open reading. But remember: an open reading on a multimeter does not prove good insulation. That's what an insulation resistance tester (megohmmeter) is for.

I skipped this check once. The cable was new, the job looked like one we'd done before, and I thought—what are the odds? The odds caught up with me. An open conductor was found only after the splicing crew had set up. Since then, the continuity check is non-negotiable.

I want to say the first time I caught a damaged conductor with this method was on a 1,100 ft Prysmian MV cable run—but don't quote me on the exact footage. The point is, it was a brand-new cable, and the continuity check found the problem.

Notes and common mistakes

Three final reminders:

• Cleat spacing. The most common mistake I see with Prysmian cable cleats is not undersizing the cleat—it's inconsistent spacing. If the design says every 1.5 m, don't stretch it to 2.4 m because you're one cleat short. The short-circuit forces don't care about your count.
• Voltage drop inputs. A voltage drop calculator is only as good as the load and length you enter. For a motor feeder, use the locked-rotor current if you're checking starting voltage, not just full-load current. A calculator can't catch a misread drawing.
• Multimeter batteries. Check the meter on a known-good circuit before you trust an 'OL' reading. A dead meter looks exactly like an open conductor. I made that mistake once. It was a $400 mistake, not a $4,000 one, but it was still annoying.

Looking back, I wish I'd formalized this checklist a year earlier. It's not glamorous. It's just the difference between a cable that works for thirty years and a cable that fails on a Tuesday afternoon. If you take one thing from this, take this: the fourth step—the continuity check—is the one that has caught the most problems in my work. Don't skip it because the cable is new.