Past a Lutron dimmer's LED limit? The power module works — but not for 18 drivers

Where this came from: this was posted on r/Lutron by u/Wired4Signs_USA_LED — not here. We replied there, in public, and this is the expanded version of that reply. The original tip is theirs and it is a good one; what follows is what we would add before anyone builds on it.

The short version

Yes, a Lutron power module is the right answer when you have outrun a wall dimmer's LED rating — the wall dimmer becomes the control and the module carries the current. The trick is real and underused.

But the headline number that usually gets attached to it — eighteen 96 W drivers, about 1,728 W, off one module — does not survive contact with the line side. Realistically you get ten to twelve of those drivers per module on a dedicated 20 A circuit. And at that scale we would not use phase-cut dimming at all.

The tip that started it

The original post made a point worth repeating: if you have installed a retail Lutron Diva dimmer and hit its LED load rating (around 150 W of LED, depending on model), the answer is not a bigger wall dimmer. Lutron makes a power module — the US part called out was the PHPM-PA-120-WH — that takes the dimming signal from the wall control and switches the larger load for you. It is rated 16 A at 120 V, and it is commercial stock rather than a big-box item.

All of that matches what we have seen in the field. The part we would push back on is the arithmetic that followed it.

Our answer

1. The load math is output watts, not input watts

Eighteen 96 W drivers is 1,728 W of LED output. That is not what the module sees. Drivers are not free — call a typical 24 V dimmable LED driver 85–90% efficient and the line-side draw is somewhere around 1,900–2,000 W, which is 16–17 A. You are at or over the module's 16 A rating before you have even looked at the branch circuit.

Then derate. Lighting run continuously is a continuous load, so a 20 A circuit gives you 16 A usable and a 15 A gives you 12 A. That is standard US practice; check it with your electrician and against your local code, because it does not apply identically everywhere.

Net result: ten to twelve drivers per module on a dedicated 20 A circuit, not eighteen. And at that point we would rather split across two circuits and two modules anyway, because it gives you a failure that takes out half the lighting instead of all of it.

We should be straight about our own hedges here: the 85–90% efficiency band is a reasonable general figure for this class of driver, not a spec pulled from a particular product. Use your actual driver's input rating if you have it — it is usually printed right on the can.

2. Inrush is the thing that actually bites

Steady-state amps are the number everyone calculates. Inrush is the number that breaks things. Eighteen electronic drivers all charging their input capacitors in the same millisecond is a serious spike, and that is what welds relay contacts and trips breakers on a cold start — not the running load.

Lutron publishes an inrush figure and a driver-count derating for these modules. We do not have the PHPM-PA sheet in front of us, so pull it before you commit to a count rather than taking our word for the shape of the problem.

Same reason, one more to check: whether the phase-adaptive module's dimming rating actually equals its switching rating. Our recollection is that these dim a good bit less than they switch, which would change the useful number again. Confirm it against the current spec sheet.

3. At this scale, stop using phase-cut

This is the part we would commit to as an opinion. Buy 0–10 V drivers instead.

Eighteen phase-cut drivers wired in parallel each have their own low-end cutoff and their own dimming curve. Some drop out at 8%, some hang on to 15%. The bottom of your range turns into a staircase — visible steps and flicker that you cannot tune out from the wall box, because the wall box only has one curve to give. This is the single most common reason a big LED install looks cheap at low levels.

0–10 V gives you a repeatable low end across the whole array and a control signal that does not care how much load is hanging off the relay. Lutron makes a power module that combines the relay and the 0–10 V output in one enclosure, and a Diva-form-factor 0–10 V wall control to drive it, so the wall looks identical and the whole class of problem goes away. We have described those without naming part numbers deliberately — confirm current model numbers before ordering, because the line has changed.

4. You do not need a dealer for this

One correction to the "dealers and commercial distributors" framing: PHPM modules are ordinary commercial stock at any real electrical supply house, and in our experience they will sell one over the counter to an electrician or a homeowner. It is not a Home Depot item, but it is not gated behind a dealer account either. Do not let anyone tell you it is.

What others said on the thread

Summarised in our words. These are other people's claims on a public forum, not ours, and we have not verified them.

• u/Wired4Signs_USA_LED, the original poster, followed up saying they had put an installation diagram on their own site for installers. Worth knowing it exists; we have not reviewed it.
• u/dano7891 described using these modules for a different reason entirely — clients swapping 6 W LED bulbs back to 60 W incandescent because they prefer the look, which blows past a RA3 Sunnata dimmer's rating. Their figure was going from a 250 W maximum to controlling 1,920 W. That is a genuinely useful use case we would not have thought to list, and it is a nicer fit for phase-cut than a big LED array is, since incandescent has none of the low-end curve problems above.

What we would need to answer this for your house

Post or send the driver model number and how many you are running, and we will do the line-side load and tell you how many you actually get per module, and whether swapping to 0–10 V is worth it for your install. It is a five minute answer and there is no charge.

Useful to have to hand:

• Driver model number and its input current or wattage rating
• How many drivers, and whether they are on a dedicated circuit
• The breaker size feeding them
• What wall control you are using now

Disclosure: we are a Lutron dealer and have been since 1999, and we do remote Lutron and Control4 work for a living.