SO and SOOW Cord Ampacity Chart: Sizing Portable Cord to the Load

Somebody calls and asks how many amps their 6/4 SOOW is good for. You could give them one number. It would probably be wrong.

The honest answer depends on three things: the gauge, how many of those conductors are actually carrying current, and what the cord is landing on at each end. Miss the second one and you can be off by 10 amps. Miss the third and the cord is fine but the circuit is not.

Here is the chart, the reverse lookup for sizing to a target load, and the two adjustments that move the number.

SOOW and SO cord ampacity chart

Ampacity for copper conductors in flexible cord, at 30°C (86°F) ambient.

These come from Table 400.5(A)(1) of the National Electrical Code. Jurisdictions adopt different editions of the code, so confirm against the edition your customer's AHJ actually enforces before anything goes on a submittal.

Two columns, and picking the wrong one is the most common mistake on this whole topic. More on that below.

What size cord for 30, 50, 60, or 100 amps

Working the chart backwards. This assumes 30°C ambient and no additional derating.

That last row is the one people do not expect. There is no SOOW answer for 100 amps. A 2 AWG cord tops out at 80 A with three conductors carrying and 95 A with two, and 2 AWG is the largest SOOW anybody stocks. At 100 A you are into Type W, which starts at 1/0 and runs to 500 MCM.

So when a customer asks for 100 amp SO cord, they are describing a product that does not exist in that family. Do not go hunting for it. Point them at Type W and you will have the right answer before your competitor finishes checking.

Why conductor count changes the answer

Here is the part that trips everybody, including some suppliers who publish charts on this.

Your customer counts conductors. The NEC counts current-carrying conductors. Those are different numbers, and the table is indexed on the second one.

A ground never counts. A neutral does not count either, as long as it only carries the unbalanced current from the other conductors. So a four-conductor cord can land in Column A or Column B depending entirely on what the circuit is doing.

Same 6/4 cord on the reel. Column A puts it at 45 A, Column B puts it at 55 A. Ten amps, and the only thing that changed was what the customer is plugging it into.

One exception to keep in your pocket. If the load is heavily nonlinear, the neutral on a three-phase wye system can carry harmonic current rather than just the imbalance, and then it does count. That comes up on data centers, VFDs, and LED lighting packages more than on a temp-power drop.

This is also why two suppliers can publish different ampacities for the same cord and both look authoritative. One of them is quoting Column A, the other Column B, and neither says which. Before you check a competitor's number against a spec, find out which column it came from.

And once you get past three current-carrying conductors, the adjustment kicks in. Four to six current-carrying conductors drop to 80% of the table value. The ladder keeps going down from there, all the way to 35% at 41 conductors or more, though if you are quoting a 41-conductor portable cord you have bigger questions.

Why cord ampacity is lower than wire of the same gauge

This one comes up every time somebody compares a quote against a building wire chart.

Six AWG THHN in a raceway and 6 AWG SOOW are the same copper. The cord carries fewer amps. Customers notice, and they usually assume somebody made a mistake.

Nobody did. Flexible cord runs on its own table for its own reasons. The conductors are bundled inside a jacket with nowhere for heat to go, the copper is finely stranded for flexibility rather than optimized for conduction, and the cord is designed to be dragged, coiled, and flexed in ways fixed wiring never is. Article 400 accounts for all of that, and UL 62 governs how the cord gets built to match.

The practical version: never size portable cord off a building wire chart. They are different tables covering different products, and the cord table is the conservative one for good reason.

And be careful which chart you are reading even inside the code. There are ampacity tables for conductors in raceway and separate tables for single conductors in free air, and the free-air numbers run far higher because a conductor hanging in open air sheds heat a jacketed one cannot. Grabbing the wrong one overstates capacity badly, and it overstates it in the direction that undersizes the cable.

The 90°C rating you probably cannot use

Every SOOW jacket says 90°C. That number is about the cord's own thermal endurance. It is not permission to load the circuit to a 90°C ampacity.

NEC 110.14(C) coordinates conductor sizing with the terminations, and the circuit gets held to the lowest-rated component in it. Most equipment terminations are rated 60°C or 75°C. If the breaker, the disconnect, or the equipment lug is 75°C, then 75°C governs the whole circuit no matter what is printed on the cord.

This is what the arguments on the code forums are about, and it is the difference between a cord that passes inspection and a cord that gets tagged.

Ask what the cord is landing on. If nobody knows, the safe assumption is the lower rating.

Ambient temperature correction

The chart above assumes 30°C, which is 86°F. Plenty of portable cord does not live at 86°F.

If the cord runs through a boiler room, sits in direct sun on a summer jobsite, or coils near a furnace, the ampacity comes down. You look up the correction factor for the actual ambient in the NEC and multiply the table value by it.

Order of operations matters when both apply. Start with the table value, apply the ambient correction, then apply the conductor-count adjustment. Do it in the other order and you will land somewhere close but not right, and close is not a defense on a submittal.

Worked example: 6/4 SOOW on a 40 A three-phase load

Start with what the customer has.

The cord. 6/4 SOOW. Six AWG, four conductors.

The count. Three phases plus a ground. The ground does not count, so three current-carrying conductors. That is Column A, and Column A at 6 AWG is 45 A.

The load. 40 A. Against 45 A of capacity, that fits, and most people stop here.

The continuous load check. If that 40 A runs for three hours or more at a stretch, it is a continuous load, and conductors get sized at 125% of it. 40 × 1.25 = 50 A. Now 45 A does not cover it, and you are moving up to 4 AWG at 60 A.

The terminations. Confirm what it lands on at both ends before you call it done.

One cord, one load, and the answer changed twice on the way through. That is why the single number nobody can give you over the phone is genuinely not available over the phone.

Voltage drop on long runs

Ampacity tells you the cord will not overheat. It does not tell you the equipment will run right.

Temp power runs long by nature. Feeding a trailer across a yard, a pump at the back of a site, a tower crane. On those distances voltage drop, not ampacity, usually decides the size, and you can be well inside the ampacity limit while the motor at the far end is starving.

The NEC recommends holding branch-circuit voltage drop to 3%, and 5% total across feeder and branch. It is a recommendation rather than a requirement, but it is the number engineers design to and the one that turns into a callback when it is missed.

So when the run is long, ask the distance. It changes the answer more often than people expect, and it is the question that separates a quote from a guess.

Three calls you will actually get

"How many amps is my 10/3 SOOW good for?" Ask what it is feeding. Single phase with a hot, a neutral, and a ground puts two conductors in the count, so Column B, 30 A. Three phase with no neutral puts three in the count, so Column A, 25 A. Same cord, and you cannot answer without the circuit.

"I need 400 feet of 12/3 for a temp panel." The ampacity is easy. The distance is the problem. At 400 ft you are into voltage drop territory well before you are into ampacity territory, so get the load and the run length and size for the drop.

"The spec says SOOW, 60 amps." Four AWG, and check whether the load is continuous. If it runs three hours or more, you are sizing for 75 A, not 60, and that is a different cord.

Where the chart stops

SOOW runs 18 AWG through 2 AWG. That is the whole range, and DWC stocks all of it.

Past 2 AWG the product changes. Type W is a 2kV portable and mining cord on extra-flexible bare copper with EPDM insulation and a CPE jacket, MSHA approved, available as single conductor and as multi-conductor from 1/0 through 500 MCM. That is where the 100 A and 200 A answers live.

If the request is for a single flexible conductor rather than a cord, that is welding cable at 600V or DLO at 2kV.

And if the letters in the callout are the part in question rather than the amps, the breakdown of SOOW, SJOOW, and SEOOW covers which designation substitutes for which. For the standards behind the whole category, see the complete portable cord and mining cable guide. Tray cable runs on a different table entirely, and that one is in the tray cable ampacity guide.

Portable cord ampacity FAQs

How many amps is SO cord rated for?

It depends on gauge and on how many conductors carry current. Across the common SOOW range it runs from 7 A at 18 AWG with three conductors carrying to 95 A at 2 AWG with two carrying.

What size SO cord is rated for 100 amps?

None of them. The largest standard SOOW is 2 AWG, and it tops out at 80 A with three current-carrying conductors and 95 A with two. For 100 A, go to Type W, which starts at 1/0.

What size SOOW cord for 60 amps?

4 AWG. That is 60 A with three current-carrying conductors and 70 A with two. If the 60 A load is continuous, size at 125% and go up.

How many amps is 8/4 SOOW good for?

8/4 is 8 AWG with four conductors. On three phases plus a ground, three conductors carry current, so 35 A. If all four carry current, the 80% adjustment applies and it drops to 28 A.

Does the ground count as a current-carrying conductor?

No. Neither does a neutral that only carries unbalanced current from the other conductors. A neutral on a nonlinear three-phase load is a different story.

What ambient does the chart assume?

30°C, or 86°F. Hotter than that and you apply a correction factor before anything else.

Can SJOOW use the same chart?

The same table covers it. SJOOW is 300V rather than 600V, so the voltage limit changes, not the ampacity math.

Why do two suppliers publish different numbers for the same cord?

Usually because one of them mixed up the columns. Check whether the chart you are reading is quoting two current-carrying conductors or three before you trust it against a spec.

Portable cord ampacity is three questions, not one. What gauge, how many conductors are working, and what it lands on. Ask those in order and the chart does the rest.

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