Why this phrase exists at all
Standard general liability policies contain an "other insurance" clause saying that when more than one policy covers a loss, they share it proportionally. That default is fine between strangers and terrible for you: it means a claim caused entirely by your plumber can be split between the plumber's insurer and yours, putting a loss on your record and eroding your limits for something you did not do.
Primary and non-contributory wording overrides that default. It is two promises: their policy responds first, and their insurer will not seek contribution from yours.
The two halves, separately
| Term | What it changes | What happens without it |
|---|---|---|
| Primary | The vendor's policy responds before any policy you hold | Both policies can be triggered at once and argue over order |
| Non-contributory | Their insurer waives the right to demand your insurer share the loss | Their insurer bills yours for a proportional share of the settlement |
Requiring only "primary" is a half-measure that shows up in a lot of older vendor agreements. It gets the order right and still lets the vendor's carrier come after yours for contribution.
How it is added to a policy
Most commonly through ISO form CG 20 01 (Primary and Noncontributory — Other Insurance Condition), or through primary-and-non-contributory language built into a blanket additional insured endorsement. Note the dependency: this wording modifies how coverage responds for an additional insured, so it is only meaningful if additional insured status actually exists. Requiring primary and non-contributory without requiring the additional insured endorsement is asking for priority in a policy you are not on.
Verifying it
The ACORD 25 has no primary-and-non-contributory checkbox. It shows up, if at all, as free text in the Description of Operations box — which means it is a typed assertion with nothing behind it unless the endorsement is attached. This is the requirement most likely to be claimed on a certificate and least likely to be evidenced.
- Read the Description of Operations box for primary and non-contributory wording.
- Ask the producer for the CG 20 01 or the blanket endorsement that contains the wording.
- Confirm the endorsement applies to the coverage lines your contract names.
- File it with the certificate and the additional insured endorsements.
This is one of five endorsement-level checks that certificates routinely fail.
See what to check on every COI