(a) No insurer shall retain net any risk on any one subject of insurance, whether located or to be performed in this State or elsewhere, in an amount exceeding ten per cent of its surplus to policyholders.
(b) For the purposes of this section, a subject of insurance as to insurance against fire includes all properties insured by the same insurer which are customarily considered by underwriters to be subject to loss or damage from the same fire.
(c) Reinsurance in any reinsurer not qualified under article 4A may not be deducted in determining risk retained for the purposes of this section.
(d) In the case of surety insurance, the net retention shall be computed after deduction of reinsurances, the amount assumed by any co-surety, the value of any security deposited, pledged, or held subject to the consent of the surety and for the protection of the surety.
(e) This section shall not apply to insurance of marine risks or marine protection and indemnity risks.