Limit is total number of policies, NAT and zones on the SRX.
The master administrator can configure a security profile for the master logical system that specifies the maximum and reserved numbers of security policies applied to the master logical system. The number of policies configured in the master logical system count toward the maximum number of policies available on the device
https://www.juniper.net/documentation/en_US/junos/topics/concept/logical-system-security-policy-understanding.html
The master administrator configures the maximum and reserved numbers of security policies for each user logical system. The user logical system administrator can then create security policies in the user logical system. From a user logical system, the user logical system administrator can use the show system security-profile policy command to view the number of security policies allocated to the user Logical system.
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